The need of a plumber in a situation like this cannot be overlooked. One thing for sure is he will end up solving the mold issue once and for all in a professional and efficient manner. On the other hand, keeping the drainpipe clean can go a long way in preventing mold from forming. It is important to note that keeping your sink clean is the only sure way of preventing mold from ever forming in drainpipes. In addition, the drainage system should be excellent because any water clogging is a contributor to forming of mold.
Regular cleaning of drainpipe should be done from time to time using the appropriate anti-fungal solutions so as not to give room for any mold to form.
The drainpipe for each must be connected to a that supplies the pipe with air from the outside. In some cases the drainpipe is connected directly to a main or secondary stack pipe, which travels straight up through the roof. More often a drainpipe is connected to a revent pipe that reaches up and over to tie into the main vent stack. Plumbing codes strictly prescribe where vent pipes can connect to the stack and how far they should travel. In most cases a "wet" section of pipe -- the part that carries wastewater -- cannot be used as a vent, even if it is usually dry.