Septic Tank Issue

Forge83

Hi, I have a concrete figure 8 septic tank. Installed approx 13 years.
It was getting backed up a bit the last year but I think I found the problem. A t-box junction leading into the drainage field was broken and Earth was blocking the pipe. It’s now rodded clear and fixed.
However, also in the last year the tank itself has sunk slightly on one side approx 3 to 4”. My question is, could this also be affecting the drainage from the tank or is it negligible? I’ve fixed the other issue about a month now and have not had an issue since but obviously we haven’t had any major rainfall which would affect the drainage field.
I’m looking to reseed the whole back garden but don’t wont to do so if it means the septic tank has to be brought level for it to operate correctly as I’d have to bring in a jcb.

longgonesilver

Has the tank sunk or has the ground settled around it?

mickdw

If the tank was perfectly level, the outlet pipe would be 50mm below the inlet pipe. This is how they are made to allow level of effluent in tank to be just below the inlet pipe and so no liquid remaining in the inlet pipe run.
If the tank has sunk on the outlet side, it may not cause any problem however if the inlet side has sunk, the outlet could now be too high and be causing the pipe from hiuse to tank to back up abit.

Forge83

longgonesilver wrote: »

Has the tank sunk or has the ground settled around it?

It’s hard to say. It could be a combination of both.

Forge83

mickdw wrote: »

If the tank was perfectly level, the outlet pipe would be 50mm below the inlet pipe. This is how they are made to allow level of effluent in tank to be just below the inlet pipe and so no liquid remaining in the inlet pipe run.
If the tank has sunk on the outlet side, it may not cause any problem however if the inlet side has sunk, the outlet could now be too high and be causing the pipe from hiuse to tank to back up abit.

Thanks Mick,
I should be able to measure this tomorrow. Makes sense.

Forge83

mickdw wrote: »

If the tank was perfectly level, the outlet pipe would be 50mm below the inlet pipe. This is how they are made to allow level of effluent in tank to be just below the inlet pipe and so no liquid remaining in the inlet pipe run.
If the tank has sunk on the outlet side, it may not cause any problem however if the inlet side has sunk, the outlet could now be too high and be causing the pipe from hiuse to tank to back up abit.

Hi Mick,
I measured them both and there is about a 40mm difference in height.
However, I checked the solids tank while I was at it. It’s about 3/4s full but half of that is water. Should the water not be displacing the water in the second tank and sending it to the drainage field?
Note there is also a gradual fall all the way from the house to the tank.

mickdw

Both parts of the tank will be always full of water to outlet pipe level. Only when a toilet flush comes in does a toilet flush worth of water trickle out the outlet pipe to percolation system.
If water to going out as expected as soon as it reaches bottom of outlet pipe, i dont see that you have a problem.
The inlet and outlet should be formed with a T piece so that incoming effluent enters the tank without splashing onto the surface. With the T pieces in place, a skin can form on the top surface with effluent entering and exiting without disturbing this preventing undue smell etc.

Forge83

mickdw wrote: »

Both parts of the tank will be always full of water to outlet pipe level. Only when a toilet flush comes in does a toilet flush worth of water trickle out the outlet pipe to percolation system.
If water to going out as expected as soon as it reaches bath id outlet pipe, i dont see that you have a problem.
The inlet and outlet should be formed with a T piece so that incoming effluent enters the tank without splashing onto the surface. With the T pieces in place, a skin can form on the top surface with effluent entering and exiting without disturbing this preventing undue smell etc.

Thanks Mick.
As I said previously, it’s been working fine since I fixed the damage t piece in the soak away pipe. So hopefully that will continue when it rains and the ground is wetter.
Yes both pipes have a t piece. No top skin and it does smell a small bit. I pumped the water tank 3/4 empty before I fixed the t piece in the soakway. Would that be why there’s no top skin in the solid tank?

mickdw

Ya if you pumped it out, it will take a short while to fill up to outlet again before you get any discharge to percolation system and any skin also wont exist.
Id just let it run now for a few months to see that all is well.
If it starts to back up in winter, well you need to start looking at percolation system.

Forge83

mickdw wrote: »

Ya if you pumped it out, it will take a short while to fill up to outlet again before you get any discharge to percolation system and any skin also wont exist.
Id just let it run now for a few months to see that all is well.
If it starts to back up in winter, well you need to start looking at percolation system.

Mick, thanks for the advice.
Greatly appreciated.