Plumbing Smell Mystery

Axolotl · 09-02-2011, 10:57 AM

We had a new septic tank and drainfield installed last fall. Ever since then we have had a VERY strong sewer smell coming from our drains and from the vent pipe on the roof any time we run much water (shower, laundry, etc). I thought the smell was coming from the new tank, so I opened the cleanout (on the drainline between the house and the tank) and left it open. Little or no odor seems to be coming out of it, even when we smell it in the house. It's almost as though the smell is coming from the plumbing inside the house, but we aren't sure how that could be possible, or why it would be happening.

1. What is causing the smell?
2. Why did it start when we got the new septic system?
3. What can we do to get rid of it? It's quite overpowering both inside the house and out.

Alan · 09-03-2011, 11:07 AM

Usually this is because of the sanitary tee installed on the inlet of the tank.

It's just the buildup of gas inside the tank, that is going back up the drain line and out the vents of your roof.

We have put plugs in the tops of them before to help alleviate the problem. We get the expandable type of plug used for testing, and just set it in there loosely so that some of the gas can still escape, but not at the same rate that it normally does.

I'm not sure why they are installing them like this. They used to be just a 90 dumping down in.

bunjamins · 09-03-2011, 11:46 AM

Possible you have any dry p traps? Plumbing fixtures from lack of use can dry out causing that p trap gas seal to be ineffective. Make sure there is water in all floor drains and that all fixtures have run some water through recently.

Otherbill · 09-03-2011, 10:53 PM

Quote:

Originally Posted by bunjamins

Possible you have any dry p traps? Plumbing fixtures from lack of use can dry out causing that p trap gas seal to be ineffective. Make sure there is water in all floor drains and that all fixtures have run some water through recently.

we had a simular problem with a rental and the plumber put a t vent on the outside drain pipe to the septic tank.

Axolotl · 09-05-2011, 07:40 PM

Thanks for the replies. I opened up a wall and did some hunting today. It appears that our shower drains do not have traps, and the washing machine drain doesn't either (house was built in 1976). As a test I've put tape over/around all the trapless drains and it seems to have helped. Looks like we could be in for some major plumbing work to add traps, as our concrete slab construction is pretty limiting.

We're still curious why this didn't happen with the old septic tank/drainfield. Someone said the new tanks are more efficient, and that therefore they produce more byproduct gas. Could this be right? If so, even after we fix the drain traps we will still have a terrible smell coming from the outside vent. Is there any thing additional we can do? It sounds like maybe the plug on the T-inlet would help.

What is the "T-vent on the outside drainpipe" you are describing? A vent added to the drainline that feeds the tank? I already have the cleanout port open on the drainline, and it isn't having much effect.

Alan · 09-05-2011, 10:14 PM

Quote:

Originally Posted by Axolotl

Thanks for the replies. I opened up a wall and did some hunting today. It appears that our shower drains do not have traps, and the washing machine drain doesn't either (house was built in 1976). As a test I've put tape over/around all the trapless drains and it seems to have helped. Looks like we could be in for some major plumbing work to add traps, as our concrete slab construction is pretty limiting.

We're still curious why this didn't happen with the old septic tank/drainfield. Someone said the new tanks are more efficient, and that therefore they produce more byproduct gas. Could this be right? If so, even after we fix the drain traps we will still have a terrible smell coming from the outside vent. Is there any thing additional we can do? It sounds like maybe the plug on the T-inlet would help.

What is the "T-vent on the outside drainpipe" you are describing? A vent added to the drainline that feeds the tank? I already have the cleanout port open on the drainline, and it isn't having much effect.

The tee is inside the tank on the inlet side.

Are you sure there aren't traps? Is it possible they are below grade / subfloor and you just can't see them?

Axolotl · 09-08-2011, 07:45 PM

I'm going to open up a wall further this weekend to verify the lack of traps, although I'm pretty sure they aren't there. Also, I put tape over all the tub drains and around the washing machine drain and it has eliminated the smell inside the house. The smell from the vent pipe remains strong.