Please help me. Whenever we turn our cental air/heat on a foul sewer like oder fills our home. We have tried everything and we can't seem to get rid of the oder. We think it may be coming from our sump pump which is in the basement about 10 feet from our fournace. We have poured bleach into the sump pump and placed deoderizors over the air filter, all to no avail.

Sounds like its time to get a good contractor in to check your system out. In the meantime be sure that the condensate drain from the a/c coil is not piped directly to your sanitary sewer system. Also be sure to pour water into any seldom used sinks, tubs etc.