I'm careful about keeping grease out of the drain but there is still some that gets washed down from residue on dishes and pots and pans and it seems to build up after time, especially in the garbage disposal. I just finished cleaning it all out and wondering where does all that stuff come from since I rarely even use the garbage disposal. Anyway, I've read that if you pour a half and half mixture of boiling water and vinegar down the drain every so often, it clears grease out of the pipes. Is this true? I also read somewhere else that it's not a good idea to pour boiling water down pipes. So, I don't know what to do, what do you plumbers say? I have typical PVC waste pipes.