The lint reacts with the water and soap, creating a frothy brew. I smell it, unfortunatley, on a regular basis. It's not the drain, there is always a small amount of water in the washer between cycles. It becomes liquid fart. A healthy amount of bleach will solve your problem. Pour abut a half gallon.

__________________
Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2