We have a terrible sewer smell that comes from what I assume is our main drain. Every time we wash clothes we get a "backdraft" that is absolutely rotten. A friend told us it was from build-up and to pour bleach down the drain. I've never encountered this problem before in any other house and wonder if this will take care of it or if we should dump some drain cleaner down it to try to remove the build-up. I can't take it much longer. Any advice would be welcome. Thanks.