The main problem of sewage is the emergence of unpleasant odors, this may be to blame for the plumber who mounted the system for you, or maybe just some details came out with expirational. The main reasons are cracks in the cuffs on the plum, poor pipe connection. You can eliminate such problems yourself, it is enough to twist the joints with the key with the key, and process the cracks with sealant, no matter what water.