This may be an odd one, but I am in a continual argument with my son, who is also my landlord. Recently my bathroom sink started backing up. Dutifully, I undid the elbow to check for build up or obstructions. Perfectly clear. Told son, he arrived with high power drain cleaner. Applied and in appropriate time drain ran clear and fluidly. Move on two weeks, same problem arising. Just mentioned it to my son and received a non argumentative response that left me a little baffled. His belief is that all of the shaving soap/cream product and stubble going down the drain is causing an almost immediate system back up. Doesn't mind I have all that "goop" but that's the reason and that's that. Obviously I am of different belief (he only shaves twice a week and states he has no problems with a backed up bathroom sink) and say there is a larger cause that must be addressed. I open it to discussion and expect to see everything from bewilderment to constructive observations (and maybe a solution that leaves both my son and me pleased).