Question:
I would like some feedback on the subject of an inlet tee being installed inside the septic tank. Alabama just started making us put them in, and I wanted to see if anyone had any problems with it.
Answers:
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In my opinion, a primary trash tank/compartment should have an inlet baffle as well as an outlet baffle. The same is true for a secondary trash tank/compartment — you need them. Otherwise, the solids and FOG will not accumulate in the tank sufficiently.
The inlet baffle greatly reduces the turbulence caused by liquids rushing into the tank and keeps the floating debris from backing up in the sewer pipe. The outlet baffle helps keep most of the floaters from leaving the tank and should pick up water from the clear zone to pass on to the next stage.
Here in Texas, we are supposed to use the baffle length into the water from the flow line to one-third to one-half the flow line depth. At least that’s what I do. I have seen no problems in septic lifetime with this approach.
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Inlet tees on a tank seem to work fine. We have used them for some time. They also make a great retrofit for tanks with broken inlet baffles. We have seen some concrete tanks with a full baffle across the width of the tank on the inlet in a low-flow situation become so thick that the sewage would not flow. With a tee, it seems to drop on down.
Occasionally one will hang some toilet paper, but that is often a result of not enough drop out of the inlet. Just make sure that you have an inspection port over the tee, because you can then clear it if it should become clogged. The main thing is to introduce the sewage in a manner that doesn’t disturb or stir the scum layer on top of the tank.
Question:
I have a question about septic odor. Over the years, some homeowners have complained of a smell outside their new homes shortly after they move in. These are homes where I installed the system. Some are gravity systems, some flood dose. Most of the homes were plumbed by the same plumbing company.
I have wondered for a long time if this plumber is doing something wrong — I don’t recall having the smell issue when other plumbers do the work. They do return when called by the homeowner but never find anything wrong. They always blame me.
The cure for the smell almost every time has been to remove the outlet tee or baffle and install a 90-degree elbow in its place. Can anyone explain why this causes the smell to go away?
Answers:
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I would want to be clear about the placement of what you describe as the outlet tee. To me, that is on the outlet side of the tank. If that is the case, then I would be reluctant to place a 90-degree elbow on this unless it had a vent drilled into it.
If you do that, though, the gas problem is likely to remain. If you use a 90 with no vent and the fall from the tank to the distribution box or dose tank is sufficient, the 90 becomes a siphon and will drain the tank to the bottom of the drop pipe. This is likely to pull more solids into the absorption area because of the surge.
Often the gas odor outside the home is just a result of vents being too low on a steep roof line or vents setting next to an outside wall that extends above the roof line. Again, the installer is not at fault, but can earn credibility for diagnosing the problem. We have had success with charcoal vent filters as well.
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As the 90-degree elbow discharges below water, the septic is prevented from venting out the house stack. The septic tank likely then vents out the drainfield in gravity systems and likely via manholes in pressure systems. It sounds like there is a P-trap missing between the house sewer and septic tank.
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The smell goes away because if the outlet of the pipe is underwater, gas from the septic tank collecting in the air space above the liquid cannot get into the pipe. This may create a new problem because gas in the septic tank now has nowhere to go. So it will probably start to stink up the yard. As for diagnosis, here are a few possibilities:
If the roof vent is too far from the fixture it is intended to serve, the P-trap will siphon dry. The roof vent is not just a vent to allow odor out. It also is a siphon break. So if the vent is too far from the P-trap, or if the diameter of the vent pipe is too small, the water in the P-trap will be whisked away.
If a home sits unoccupied for a while, the water in the P-traps can evaporate. In floor drains there are common locations where plumbers omit traps. I have no idea why. One section of vent, because it is installed vertically, can pull away from another if they are not connected correctly.
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I can’t believe a P-trap underground in the line outside of the house. If it was up here in Alaska, it would freeze, which is just one more reason to not have one. I can’t in my wildest imagination figure out why anyone would put a trap in the line between the foundation cleanout and tank.
Do they vent the tank through the pumping risers? It’s got to be vented somehow, to somewhere. I’ve had a few of those with odor inside empty P-traps, but they’re usually with a rarely-used shower or hidden floor drain in the basement or a washing machine dump in a spare room that never gets used.
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I install all piping from two feet outside the house to the tank and beyond. I use Schedule 40 pipe with all fittings primed and glued. All pipe is bedded in stone, with extra care in the overdig of the basement. We install a cleanout on every home. There are no P-traps. The tanks that I used were concrete. They came with a plastic baffle on each end. These baffles were plastic (about 12 inches square, extending down 12 inches below the invert), bolted to the sides of the tank.
The odor usually was very noticeable and occurred almost immediately. Of course, most home-owner complaints came during the warm months. Plumbing vents through the roofs were changed on several of the homes. This did not help. Here in Indiana, we are required to leave the risers on the tanks extending to the surface.
Several homeowners were sure that this was where the smell was coming from and covered the risers with plastic to seal them. This did not help. I am still not sure why the smell stopped when a 90-degree elbow was installed on the outlet end of the tank. We tried a 90-degree elbow on the inlet end of several tanks (against our better judgment). Only once did this help.
