I studied somewhere that a septic tank should have 2 buffer walls so one side water enters and all the sludge settles down in first chamber and the water that overflows above the first buffer wall is somewhat cleaner now the second chamber's water has some what lesser particles and the water that overflow the second buffer wall will be free of particles and filtered water goes to last chamber and from last chamber water is taken away using a outlet pipe to soak away.

So the problem here is I have both inlet and outlet on the south side of building because North side has concrete structure, west side is kitchen and east side there's no space left.

Outlet pipe is always sealed and meant to be used by motor from tanker lorries.

Now my question is

  • Do I need two buffer walls ? I'm not seeing any reason
  • If there's no buffer wall , then will it affect bacterial growth ?

If buffer wall is necessary then how all the sediments can be removed from motor pump of tanker lorry , the sludge would get settled forever.

  • 2
    The outlet from a typical septic tank discharges treated water into a drain field, and the sludge is only occasionally vacuumed from the bottom. If your septic tank doesn't have an outlet (so even the treated water stays inside and needs to be tankered away), it's not a septic tank but a cesspool.
    – TooTea
    Dec 16, 2021 at 15:16
  • 1
    Yeah that makes sense
    – CuriousMan
    Jul 13, 2022 at 6:41

3 Answers 3


I'm not a septic system expert by any means, but getting buffer walls in your tank with both the inlet and outlet on the same side of the tank is simple. In theory...

You'd need a full height divider wall between the inlet and outlet that runs almost the full length of the tank, then put the buffer walls on the inlet side. This will force the water to go over the top of the buffers as it works its way from the inlet to the outlet and not let it shortcut directly to the outlet.

Something like this excellent ASCII art:

|                          ->
| =========================|
|     i           i        |
|     i           i        <-


  • ->: Outlet
  • =: Full height divider wall
  • i: partial height buffer wall
  • <-: Inlet

As water comes in the Inlet from the right, it's forced over the buffer walls then finally makes its way all the way to the left where it can go around the end of the full height wall (note, there is a gap there in the drawing) and begin its journey back to the right where the Outlet is.

I'm sure that this will not be an inexpensive change to make or even if it's possible to modify an (your) existing septic tank. It might require a full replacement and possibly a custom design. It is however a solution and sometimes, you just have to fork over the cash to get a workable solution to a problem.

  • 1
    If you're going to alter the inlet icon, may as well have altered the outlet icon, too, @r13... :/
    – FreeMan
    Dec 16, 2021 at 14:39
  • 1
    Yes, it looks more clear now.
    – r13
    Dec 16, 2021 at 14:50
  • The sediment from the sludge will completely cover the ground and it'll prevent water discharge through the ground. The outlet pipe is meant to be used as way for the motor pump's pipe to enter and get all the liquids along with sediment out to tanker lorry as there's no public sewage line.
    – CuriousMan
    Dec 16, 2021 at 19:14
  • 2
    In theory, @RaviMan, most of the sediment will have dropped out of the liquid as the liquid flowed past the buffer walls. Sure, earlier parts will fill with sediment, but that's what the biology living in the septic tank is for - breaking down that sludge. TBH, I'm now past the end of my knowledge of septic systems. My main point in the answer was to show how you could get two buffer walls in a tank where the inlet & outlet were on the same side of the tank.
    – FreeMan
    Dec 16, 2021 at 19:17
  • @RaviMan - I think bacterias will eat away all the sludge and if you leave it long enough without using toilet .. you might find septic tank water as clean and without any foul smell and the extra well could increase the biological activity
    – Amogam
    Dec 16, 2021 at 19:26

I'm not sure about bacterial growth

All I can say is buy and install a better filter on the sides of outlet pipe

so no solid goes away only pure liquid goes away and your problem is sorted and you may redirect this filtered water to leech field or something else.

Make sure the filter that you buy won't get clogged with solids search and find better filter ,, I don't know any filter name

  • Thanks for suggestion , filter name could have been helpful and I don't want bacterial growth to get affected at any cost so would like know some authoritative answer in this
    – CuriousMan
    Dec 16, 2021 at 10:46
  • 1
    The simple reasons for the need for baffles are 1) lengthen the travel path of the wastewater that provides a better chance for settlement to occur in a size down manner, and 2) to cause small turbulence of the still wastewater to inject oxygen that is required for the good microbes to grow (check me on this) and eliminate/minimize the smell. The coarser particles will settle in the first chamber, the finer the next. It is not rare to have two cleanouts for settlement removal. FreeMan posted a good idea which shall be followed.
    – r13
    Dec 16, 2021 at 14:31
  • @r13 - Thanks. I saw the diagram that makes sense..
    – CuriousMan
    Jul 13, 2022 at 6:46

Generally speaking most residential tanks installed today only have one baffle, though building and sanitation codes may alter that depending on region. Also, depending on the tank design, there can be a baffle specific to the outlet for the purpose of providing additional protection to the drain field or d-box from solids passing into those components. Within the tank, the purpose of the baffle is to allow controlled migration of the treated waste from the entry chamber of the tank by creating a barrier designed to prevent the migration of solid waste that has not yet been decomposed from flowing into the effluent chamber of the tank and ultimately protecting the leaching component of the system (drain field) from infiltration of solids which will shorten its lifespan.

Q: If buffer wall is necessary then how all the sediments can be removed from motor pump of tanker lorry , the sludge would get settled forever.

A: The baffles do not cut off the flow of effluent moving through the tank, they only serve to mitigate the movement of solid waste into the effluent components of the system. With regard to the tank itself, the truck pumps the solids from the entry chamber - but there should be access for them to do so in the effluent chamber in the event that the system has been overloaded.

I'm not sure what you are trying to accomplish given your other questions on this subject, except that you are either trying to design an onsite residential waste treatment system or you have a failed system you are trying to repair. It would be helpful to have better context on the whole problem you are trying to solve.

If you are trying to design a system, and your region allows individuals to do so (in my region you must be a certified engineer), you may want to start with a google search using the following phrase "modern septic system designs".

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.