I had a septic tank delivered and want to understand what needs to be done for the hookup (I'm not doing it myself, just want to be sure I understand the requirements).

I'd seen / read that you usually build a sort of sideways T structure at either end of the tank with the lower end of the outlet T higher than the lower end of the inlet T-- but this tank seems to have built in baffles already at both ends-- does this not need that structure, and you just plumb a straight pipe in?

Inlet Struture Outlet Structure

Second question is how does the pipe get sealed when it penetrates the box? Is it some sort of mastic / sealant? Or is a friction seal good enough since the fluid level probably wouldn't get this high



EDIT: I'm just asking about the inlet / outlet baffles as shown in this drawing (not drainfield size or interior baffles in the tank itself). The tank seems to have something already installed, and I'm not sure if this is the case or if they tank still needs these baffles installed.

enter image description here

  • The requirements will vary depending on location. Check with the installers and the local inspectors.
    – JACK
    Jul 23 at 18:57
  • The size of tank and location have requirements but I don’t see a baffles. , the area , size of building or number of bathrooms / bedrooms define the size of the tank and drain field , the tank baffles are different than the surface baffles as your pics show, so more information is needed.
    – Ed Beal
    Jul 23 at 19:08
  • @EdBeal I edited the question to show the baffles I'm asking about. The tank seems to have them pre-installed, but I've never seen this before so I'm hoping someone knows. Thanks
    – user101289
    Jul 23 at 19:14
  • 1
    The piece of steel looking and the other plastic looking objects would be called baffles. If your local health department agrees is another matter, they have the final say
    – crip659
    Jul 23 at 19:22
  • The tanks that have been required in my jurisdiction required 2 chambers. A wall was between the chambers and most of the solids drop out in the first chamber that is what we called baffles the inspection covers allowed the tank to be pumped and for the last ~20 years a sealed shaft and manhole cover has been required to the top of the tank on the sediment side.
    – Ed Beal
    Jul 24 at 0:15

1 Answer 1


The plastic (which is tapered) around the pipe holes should seal when a pipe is pushed through it. Cut out the center neatly (your contractor should be experienced with this detail.)

Assuming your LAHJ agrees, the tank does appear to have baffles, though I'm sure the tank supplier could confirm that (and that the outlet baffle is also a filter) if you ask them. One aspect that the inlet baffle solves is that Tee baffles made as illustrated are prone to clogs - I went with 6x4x6 tee for that part on the advice of my LAHJ, as they claimed that had much fewer problems with clogging than 4x4x4 Tee for the same use. Your steel inlet has considerably more area than a 4" pipe, which achieves the same end, and if it's all stainless and properly fastened so it does not fall off in several years, it's less subject to breakage than a hunk of pipe is.

The presumably/hopefully stainless steel appears to be the inlet baffle.

The more complex structure at the other end appears like it might be a filter (which is a good thing to have on the outlet) and baffle in one - there should be access from above there as well to inspect/clean it. Of the two, that's the more important one to have a permanent riser to ground level and manhole cover for - knowing where the tank is from that reference, you can get to the other end if needed with a shovel, but you would very rarely need to. If your LAHJ requires a riser at both ends, you do that to keep them happy. Regular maintenance (clean filter and pump out sludge) can all be done from the outlet end.

If the presumed filter has provisions to add a handle (typically made of small diameter PVC pipe) you'll want to do that before the tank is placed in service, extending up into the riser above the tank.

  • Thanks-- that's very useful. There is an inspection port above the outflow baffle, though there isn't a filter in there. I'm in N Idaho, and I don't think that's code here (as far as I know anyway). The inlet baffle is actually heavy plastic, not steel, but it's screwed to the wall of the tank with stainless screws, it appears.
    – user101289
    Jul 24 at 2:17
  • Whether or not code requires it, an outflow filter is good practice. Keeps things that should not be in the drain field out of it, and far better to plug a filter that can be removed and cleaned (and get you to pump the tank) than to plug your drain field that requires a backhoe to fix/replace. They've been an established technology for a couple of decades now.
    – Ecnerwal
    Jul 24 at 11:47

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