On 3/24/2017 4:02 PM, Bob wrote:
I just bought an old farmhouse (really good deal) an am going through
all the repairs that need to be done and now have a puzzle.

When a large amount of water is flushed down the pipes (i.e. bathtub
emptying) the basement fills with sewer gas. Found a clean-out cover
rusted out (and now fixed) but still having the gas odor.

I think that when the waste water enters the tank, the gas gets pushed
back. After the fix it has dropped noticeably, but it appears it has now
been directed to the tank vent.

There's still some gas in the basement, and a fairly good stench from
the septic vent, have I been living in the city so long to forget that
this is normal?

Agree with other comments. My tank is not vented but house vents should
take out odor. Traps should be filled and vents clear.