Septic Smell in basement


Well-known member
Apr 3, 2016
Baltimore MD
Anyone have a septic system? Ever encounter this? When the weather gets rainy or changes, our basement gets a septic yuck smell. Not feces smell (sorry!) but just a smell that I associate with septic.

I've had a plumber come out multiple times and all he does is seal up the black "man hole" looking thing in my basement in the concrete floor. He caulked it closed. Clearly not air tight.

Researching this myself a bit I see that there is some sort of water trap in there that might have dried out (not near a toilet, the smell isn't coming from a toilet) and that I should be adding water to this hole to stop the septic gas from coming in. Seems the opposite of what my plumber did by sealing it off. If i need to add water, how can it be sealed tight?

Any thoughts?


Mod Squad
LifeTime Supporter
Jul 10, 2012
Tallahassee, FL
I have a septic system. When we have more that a days rain as in 2 or 3 days of rain we get the same smell. It comes in through the back bathroom tub. We just pour some bleach into there and it goes away. That tub is also the one that is closest to the the septic field. I guess that goes along with what you have read.



Well-known member
Apr 3, 2016
Baltimore MD
I would understand this better if our smell was coming from the tub or the toilet. When the toilet/tub isn't used much i guess the pipe can dry out and gas can come back through it. It must be the same logic with my "manhole" thing. However, ours is sealed so I can't add any water..

I guess I should have the plumber come out and take a look myself when he opens it up.

I made a point to ask the company who checks our septic field/tank biannually whether I should smell this and he said no way - no smell should be in the house, according to him.

So frustrating!


Pool Tool

Well-known member
May 15, 2014
Western Chicago Area, IL
If you have a water trap you suspect is drying out, you can pour in enough vegetable oil to fill the trap. In theory, oil being lighter than water, the oil will float on top of the water and stay in trap then also not evaporate like water would. In reality, you will have to replace the oil occasionally but at much longer intervals than replacing the evaporating water. The oil will then prevent the sewer/septic gases from getting thru the trap.


Well-known member
Apr 27, 2013
Wichita, KS
I've never had a septic system, but I've had several sumps. Could the "manhole thing" be a sump? I've never seen one get sealed off, nor have mine ever smelled...
I have a sump in the basement that was sealed off during a radon abatement procedure when we bought the house. The cover does have a vent in it that is about 1 1/2".