My neighbor has a sump pump pit that her washing machine empties into via a laundry tub sink and a sump pump automatically pumps it out to the septic tank leaving a bit of water in the bottom of the pit. The line from the sump pump goes about 3" above a line from the kitchen and bathroom sink at the basement ceiling and then downward tees into this line which then goes to the mainline to the septic tank. The septic tank mainline is a few feet below this sink drain line. In the past few months there has been an odor in the house, basement primarily, that seems to be coming from this area. Doesn't smell like a sewer smell but, IMO, more like a vinegar cole-slaw smell. Strange thing is this setup has been in use for over 40 years and is just now becoming a problem.
She had a one-way trap put on the pipe from the sump pump to the septic tank in case the water level was dropping too low in the pit and uncovering the pipe end but this doesn't appear to have helped much (yet?). There are no other plumbing issues in the house. She has put some bleach in the pit and may use a little on some laundry days but being on septic tank it isn't overdone.
I know this is vague but has anybody experienced this or have any ideas?
Thanks.