Hi there. I did a search on your site before posting this and the only thing I found that was anywhere near similar was something I found on your old forum:
Posted by Vicki Stearns on June 11, 2002 at 14:52:34:
I have been noticing a odor coming from the area of the washing machine. Can sometimes smell it in the rooms opposite the wall of washing room. Some times you cannot smell it at all and other times it is very strong. Almost a mildew smell. Also when the washing machine has been used a couple of times in a row it is strong and also when the tub on the other side of the house is drained it smells in laundry room. No other drains or rooms have that smell. I live on concrete slab and the house is approximately 28 years old. Getting to the plumbing is awful--floor would have to be jackhammered up. Help. Any ideas what the odor may be. Septic tank was emptied when I bought the house in 1998 and I usuall live alone except when my grandkids or kids stay with me. thanks.
I have noticed these same things:
  • odor coming from the area of the washing machine
  • sometimes smell it in the rooms opposite the wall of laundry room
  • sometimes you can't smell it at all and other times it is very strong
  • almost a mildew smell
  • house on concrete slab
At first I thought it was cigarette smoke coming through the vent behind the washing machine because it seemed like the smell started when the new neighbors moved in a couple months ago. (They smoke outside between the two houses.) I've since decided that's impossible because the smell doesn't quite go away and it really seems to be a somewhat mildewy smell. Upon looking at the floors with a flashlight, I don't see any wetness at all.

I also found this reply to the aove quote:
Posted by Gary Swart on June 12, 2002 at 08:49:15 in reply to Vicki Stearns on June 11, 2002 at 14:52:34:
Just a thought, is there a Pee trap on the pipe the washer drains into or does it just go straight into the drain? If there is no trap, put one in and that should cure the problem. If there is a trap, I don't know.
I don't know what a Pee trap is, but my Dad suggested pouring bleach down the drain. Any help you could provide would be gratefully taken. Thanks.