Septic odor in my downstairs half bathroom

[Ashley B]

I am getting a mild septic odor in my downstairs bathroom. It is only a half bathroom, has a toilet and a sink. There is no other bathrooms or plumbing areas that have the same odor. I have a newer home, built in 2008 that is on a septic system. A little about the system.

1000 gallon spetic tank, 1000 gallon pump chamber. I have a Sand Lined Trench system that is on an automated low pressure distribution system. I have attached the asbuilt as well below.

This bathroom is used several times a day, the P-trap is not dry, and I have flushed it several times over the last week to no avail. I've read about some posts about pouring chemicals down the drain, but I am hesitant to do so and kill the bacteria in my septic system. There are no other slow drains or blocked drains in my house. I can't speak to the vent working properly as I believe it vents out my roof on the second floor and I haven't been up there before.

What are some of the potential causes for this odor? I am relatively handy, don't mind getting dirty, wet, or sewagy(is that even a word?) if need be. I also have the septic field layout but I didn't think that'd be pertinent to this post.

 

[Rickyman]

Pull and reset the toilet. A failed wax ring will allow sewer gas into the bathroom.

 

[Ashley B]

Thank you Rickyman, I was contemplating this but wasn't certain. I will go get one and get it replaced today. Should be able to report back in a couple hours.

 

[TomFOhio]

Also do you have a floor drain in the bathroom. If so does it have water in its trap.

 

[Ashley B]

No floor drain in the bathroom, all linoleum other than the toilet drain hole, and ofcourse the sink p-trap and drain. I just installed the wax seal about 5 minutes ago, so going to let the room sit for a bit and see if it still smells. Should know by tomorrow AM if toilet wax seal was the fix needed.

 

[Ashley B]

So I've replaced the wax seal, and it doesn't seem to have fixed the odor. After having doing some serious smelling, it really seems like the smell is coming from the sink. I removed the p-trap, and attached PVC piping that was removable, cleaned it all in the dishwasher with soap and water, verified it's VERY CLEAN, and reinstalled it. The sink STILL smells. It really seems to be coming from the overflow piping in the sink, so I plugged the sink and filled it completely full of water til it started overflowing through the overflow drain hole on the sink, flushing hot water(not boiling) and soap down this portion of the sink. After cleaning it all up and allowing it to sit for about an hour it still smells bad through the sink. How else should I go about addressing this?

 

[jeffmattero76]

Not an expert, but have you tried spraying some bleach into the sinks overflow hole?

 

[CT18]

Is there an AAV in use somewhere on the vent system. Any work in the area lately that could have put a hole or broken a vent line.