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Advice Needed: Slow Emptying Toilets & Septic Tank System

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Hi all,

Really praying somebody can point me in the right direction to resolve a 3 year problem (ever since our new house was built).

Details:

We have 5 toilets: 3 upstairs, 2 downstairs (but only 2 adults and one child live in house)

The upstairs toilets all empty slower than the downstairs one.

One upstairs toilet on average takes 10-12 seconds to empty (it is only toilet prone to get gas build up and when allowed out emptying improves by a few seconds (until next day)

The other 2 upstairs take approx 6 seconds to empty

The 2 downstairs take approx 3 seconds

We have ONLY the 5 toilets (NOT Basins, kitchen sink,showers & bath) connected to ONE 1200 litre septic tank (make unknown) Form the Septic tanks's oulet pipe there is pipe (approx. 4 metres in length) which connects to a below ground concrete rings drainage container and that connects to another concrete ring container approx. 0.5 metres from the first.

The toilets are NOT connected with the western fitting system of drainage pipe, adaptor and wax ring to make seal. Instead they seem to be toilet sewage pipe into small hollow and toilet placed above hollow. It is cemented (or whatever)into place to form a seal and stop water escaping (all toilets are 100% water tight when used).

I will ignore deep into Monsoon season when toilets do not empty for an hour or so after rain has stopped (this I am sure is water table rising and filling concrete ring drainage containers and septic tank.

MY FINDINGS & SUPPOSITIONS.

At first I was convinced clogged pipes or build up of "stuff" in below toilet chamber/hollow was the problem

or

pipes leading to septic tanks going upwards causing them th be full of water all the time causing resistance to water leaving the toilets.

HOWEVER, I recently decided to drain the septic tank (never seemed totally full). This turned out to be extremely informative in my search for resolution. The second the Septic tank was drained empty the drainage men asked me to flush all toilets to see if any improvement.

The results were spectacular with all 5 toilets including the worst upstairs toilet empties almost instantaneously (seemed like 1 second). When each toilet was flushed we all could here the water dropping into the empty Septic tank (could not see anything as black and behind a baffle board).

Now I am NO PLUMBER but this told me 3 things:

1) None of the pipes from each of the toilets are blocked or partly blocked.

2) Even if any of the toilet sewage pipework under the ground running around the house leading to the septic tank inlet pipe are not level or are slightly sloping upwards in places this make NO EFFECT to the emptying ability of all 5 toilets to the Septic tank.

3)The worst upstairs toilet has pipes travelling farthest around the house to the septic tank and yet it emptied IMMEDIATELY now.

NOW THE EXPECTED DISAPPOINTMENT.

All toilets worked perfectly for 15 days. During those 15 days the Septic tank was not full to its normal level and water could be heard dropping into it upon flushing a toilet (I monitored constantly).

AS SOON as I could no longer hear water dropping into the septic tank the emptying of the toilets slowed dramatically, but not as slow as just before we drained the Septic tank 15 days previously. As the water level rose to its normal height in the Septic tank (over the next 2 days) we were back to the usual poor emptying problems of pre emptying of the Septic tank.

I really do not understand what is going on.

1) Why are the upstairs toilets (with extra gravity drop) worse than the downstairs ones.

2) One upstairs toilet is directly above a downstairs one which is only 1.5 metres (at ground level) from the septic tank. It should be the best being so close and with a long vertical drop from upstairs

Thoughts

1) Would an inlet pipe extension pipe going down inside the Septic tank (like many septic tank designs) cause water pressure in the Septic tank to cause resistance to flushed toilet water?

2) Is it possible the Septic tank inlet pipe is lower than the outlet (therefore causing it to be slightly below the water level in the Septic tank? If this is the case maybe water has back flowed into the just below ground pipes from the toilets. This I am guessing may cause resistance as 2 of the 3 upstairs toilets are the farthest away from the Septic tank. (but one is directly above a downstairs toilet that is MUCH better)

3) Why do most of the Septic tank designs in Thailand have the inlet pipe extending down into the Septic tank by about 0.25 - 0.5 metres below normal Septic Tank water level?

Will this not cause back pressure to incoming water from the toilets?

4) Logic (well MINE anyway :whistling: ) suggests to me that PROVIDING the Septic tank inlet pipe is above the Septic tanks normal water level (and the outlet pipe is at normal Septic tank water level, then when toilets are flushed there cannot be ANY MORE resistance than when the Septic tank was empty (with of course inlet pipe above water level).

Advice received from 3 Thai Plumbers :crying:

Well I will give them one thing. 100% consistent. Ignore what I am telling them and "its how we always do it" mentality

I was told:

1) You should not have had only one Septic tank for 5 toilets. You needed 3, each close to the part of the house where the toilets are situated.

2) Due only having 1 Septic tank many of the pipes are too long for the toilets to push the water when a single toilet is flushed.

3) The pipes under the ground may well be sloping upwards towards the Septic tank, therefore the pipes are always full of water and this severely slowing water entering the Septic tank. The longer the pipe the greater the effect.

I pointed out to each of them:

1) ALL toilets emptied perfectly and immediately the Septic tank was emptied with the inlet pipe above water level inside the Septic tank. Therefore 2) and 3) could not be correct (unless the Septic tank inlet is under normal Septic tank water level).

2) One correct capacity Septic tank should work perfectly well if system installed correctly. Having 3 separate Septic tanks situated near toilet groups should not be necessary.

3) I pointed out the second worst upstair's toilet is one of the closest to the Septic tank(1.5 metres at ground level), which suggests proximately to the Septic tank and short pipes has not helped.

Well I kept pointing these facts out to them and they kept saying the same things over and over again, despite the fact I had disproved THEIR theories and explained why. I decided not to let them loose on resolution

Observations:

I have noticed that the Septic Tank outlet pipe (outside Monsoon time) seems nearly all the time to be around 6-8 cms above the Septic tank normal water level.

This confuses me and makes me wonder if the Septic tank has a crack(s) in its sides/base.

That would not surprise me because the builder in his infinite stupidity waited until late Monsoon to dig the hole and put the Septic tank under ground. He did not place a concrete base below the Septic tank (as he should have) AND as the hole filled with water due to height of the water table in Monsoon his men tried levering the tank downwards into place(of course the water kept it buoyant). The result was they cracked the entrance to the Septic tank and had to wait until a week or so into the dry season. I insisted on a new Septic tank, but as builder broke due to bad costings for building the house he ignored me saying his remedy would be 100% effective. The remedy was placing the Septic tank 15cms lower into the ground and to make a new lid surround concrete ring on top of the entrance of the Septic tank so that could be used to insert the cover.

One final piece of info Due to a 3 months bad back I have not been able (yet) to lift the lids of the 2 concrete ring drainage containers to see what the situations are inside, nor have I dug around the Septic tank to take a look at the inlet and outlet and gas release connectors and pipes of the Septic tank nor have a viewed yet, the pipe leading from the Septic tank outlet to the 1st concrete ring drainage container (to check pipe slope) and th pipe between the 1st and 2nd concrete ring container is lower than the 1st inlet pipe and slopes down to the 2nd. This I intend to do when rains abate for a week or so.

My intention at present:

Wait until a month or so into the next dry season. Get the existing Septic tank dug up and replace it with an 1600 litre tank. Then make sure the pipes in and out slope in the correct directions and make sure the inlet is higher than the outlet.

HOWEVER, I am hoping some who understands Septic tank plumbing, drainage and toilet systems in Thailand, will be able to advise me on the (long sorry) contents my post and problems. I do not want replace the Septic tank etc. and find myself in the exact same position as I am in now and have been for 3 very frustrating years.

My thanks to all who have read this past.

Hoping someone can explain what I have failed to realize and can point me in the right direction for final and 100% resolution.

Kind Regards

Dave

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Ok Dave, that was quite a read and to be honest I skimmed most of it. I think your problem is in the venting. In western countries the toilets are vented at the toilet via a stack that goes out thru the roof. In Thailand they vent the septic tank. Check to see if the vent from the septic tank is plugged as of course for water to go into the tank it has to displace air.

I am just building a house and because of the way they vent septic tanks here I did all the plumbing myself and vented the toilets themselves.

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Ok Dave, that was quite a read and to be honest I skimmed most of it. I think your problem is in the venting. In western countries the toilets are vented at the toilet via a stack that goes out thru the roof. In Thailand they vent the septic tank. Check to see if the vent from the septic tank is plugged as of course for water to go into the tank it has to displace air.

I am just building a house and because of the way they vent septic tanks here I did all the plumbing myself and vented the toilets themselves.

Hi,

Thanks for replying,

Yes there is a vent pipe from the Septic tank. I have blown down the the pipe that allows gas to vent out of the Septic tank and it is not blocked between it and the Septic tank. Consequently I do not think this is the problem.

I agree with your decision the vent the toilets which seems to me the best option if available.

Regards, Dave

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Ok, well without knowing the exact way all the waste pipes inter-connect and then flow thru one pipe into the septic tank, it is hard to guess at where the problem is. It is true that in most Thai builds they put one septic tank in for each toilet, again I believe that is due to improper venting and that is how they solve it. Do the toilets gurgle when flushed? Is there air bubbles coming back as the water goes down?

Sorry to keep harping on this, but I still think it is an air/venting problem somewhere.

Good luck

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I agree with Dave's assessment as well. take a look at your roof line & see how many vent stacks (pipes) coming -hopefully through the roof or if it is Thai style build it will be lower on the walls going towards the top. You should have probably 4 0r 5 more being better.

The best way for any septic system is to run as many lines direct to the inlet avoiding 90 degree bends even a 22 degree bend will hamper the flow & slow down the progress to the tank itself.

most likely the reason why you need more than 1 tank. I would think 2 would be a minimum on 3 toilets used regularly leaving 2 as guest style rooms with not much use. As important as that is if the 4'pipeoing to the septic is not a 40-1 slope for every 40 meters the pipe needs 1 meter slope Mine is a 40-3 & 1/2 install the more angle of the dangle in septic runs the better.

If you have adequate venting I think you would be best off to figure out how the actual plumbing lines to the septic system are hooked up. Eliminate any un-needed bends. For sure consider a second septic tank.

But most likely the problem is in your venting.I have seen some pretty piss poor vent jobs up here that actually defeat the way of the design that forces air down the stacks.

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the more angle of the dangle in septic runs the better.

Actually beardog too much slope on a waste pipe is almost as bad as too little. You want enough slope to drain, but not so much that the water all rushes away leaving the turds sitting high and dry in the pipe. When I installed my waste pipes I used about a 1/2 bubble slope on a 2 foot level.....mind you my runs were very short, about 2 meters max.

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If you open the septic tank cover, and the toilets still flush slowly, it

is NOT the venting (which was my first guess as well). In my house,

I have venting on the septic tank AND in my house (roof outlet).

It is really important to know the slope from the house to the septic

tank. If the slope is not at least 10% towards the septic tank (or negative)

you will have the situation as you describe ....

Good Luck,

rudi

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Well I am not a plumber and so.....

I have installed a similar set up as you describe but only one up and one down and have a plastic septic tank vented (2") only at the tank both toilets feed one sewer pipe and it does have a 90 degree bend...yet no problems as yet..

I think if I would have this problem I would first check the downstairs toilet standing water level when I flush the upper ones..it seems logical from other posts that if there is an air lock at the tank the water level would rise in the downstairs toilets.( I would also turn off the water supply to the lower toilets flush 'em so no water in the toilet)? From your post I would guess that you have already done this as part of your quite thorough investigation...but if the upstairs toilets are draining slowly the the water /waste is obviously not voiding the piping and backing up..?

It does sound like the lower toilets have the water level of the downstairs toilets almost at that of the septic tank ie the slope is insufficient or

since everything is fine with the ST empty....have you checked the outlet of the primary ST? ie does water run out when you flush.. where to?.. secondary tank? Is it maybe always "too" full? Is it vented also?

Since the downstairs toilets are fine it does seem that the issue is with the ST

one final thing have you flushed up and down toilets at the same time to see what happens?

BTW I used the wax rings on our toilets...brought them from Canada ...dollar stores are great!!

Good luck...shitty problem

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If you open the septic tank cover, and the toilets still flush slowly, it

is NOT the venting

That's a good theory, but a bit flawed. Actually you need the air (vent) at the opposite end of the drain. Think of it this way, take a drinking straw and fill it with water. Plug both ends with your fingers, then release the bottom finger, it will drain but air needs to travel to the top to allow that. Release the top finger and it drains quickly and easily.

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the more angle of the dangle in septic runs the better.

Actually beardog too much slope on a waste pipe is almost as bad as too little. You want enough slope to drain, but not so much that the water all rushes away leaving the turds sitting high and dry in the pipe. When I installed my waste pipes I used about a 1/2 bubble slope on a 2 foot level.....mind you my runs were very short, about 2 meters max.

My runs are close to 40 meters First house here 4 years old now (torn down)Never had a clogged toilet New house 1 year old same. In lake Tahoe (California)any septic system mandatory pipe slope is exaggerated.Even in San Francisco the plumbers agree more slope better. But I was only in the trade for 17 years so if you are more experienced you may no something I don't.I always go overkill & with double U-Traps in the system never a chance for stinky pongs to come back up through the lines. Also why I chose to blast the water through. The toilet acts the same as any other toilet except you do not get any clogs & will actually work in unison with the vents. I can see in a short run you wouldn't want extra slope but on a longer run it is OK to optimal. That is why the codes & any other info sites say a Minimum of 1 in 40. I like to make my system bulletproof. that way the only time I have to lift the lid in 30 years is when the dam_n tractor guys run over the lid.

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double U-Traps in the system
??

You mean you use another u-trap in the actual 4 inch waste line? Besides the u-trap incorporated into the toilet itself?

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I agree with Dave's assessment as well. take a look at your roof line & see how many vent stacks (pipes) coming -hopefully through the roof or if it is Thai style build it will be lower on the walls going towards the top. You should have probably 4 0r 5 more being better.

The best way for any septic system is to run as many lines direct to the inlet avoiding 90 degree bends even a 22 degree bend will hamper the flow & slow down the progress to the tank itself.

most likely the reason why you need more than 1 tank. I would think 2 would be a minimum on 3 toilets used regularly leaving 2 as guest style rooms with not much use. As important as that is if the 4'pipeoing to the septic is not a 40-1 slope for every 40 meters the pipe needs 1 meter slope Mine is a 40-3 & 1/2 install the more angle of the dangle in septic runs the better.

If you have adequate venting I think you would be best off to figure out how the actual plumbing lines to the septic system are hooked up. Eliminate any un-needed bends. For sure consider a second septic tank.

But most likely the problem is in your venting.I have seen some pretty piss poor vent jobs up here that actually defeat the way of the design that forces air down the stacks.

I've never seen any soil stacks vented on a Thai built house, only the septic tank vented, usually under the kitchen window as on my mates place!

My theory is the lack of vented soil stacks is the cause of the bad smells in many houses and condos, as well as floor drains and showers not being trapped.

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My theory is the lack of vented soil stacks is the cause of the bad smells in many houses and condos, as well as floor drains and showers not being trapped.

And you would be most correct in that theory

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another thought...if the op empties the second upstairs toilet without letting it refill ( turn off water or jamb the float "up" ) the second toilet would then become a "vent" If the first upstairs toilet still flushes and empties slowly then there is a blockage!..Note that the op said he could hear it draining when ST empty...the diameter of the pipe would suggest just be one whoosh not a draining sound??

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Beardog,

I have attached a link that describes what I was talking about and here is the specific section:

House sewer pipe should have a slope between 1 percent and 2 percent. This is around a 1- to 2-inch drop in 8 feet. On too flat a grade, the liquid will slow down, allowing the solids to settle out in the sewer pipe. On too steep a grade, the liquids will flow away from the solids.

Here

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BANGKOK 24 July 2017 19:48
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