i've been having a number of plumbing problems:

my bathtub drain has been spitting up a viscous black, sulfuric substance, grease and whatever has accidently gone down the kitchen sink, whenever i turn the water on in the kitchen. i know my drain is clogged, maybe not fully, but it is very very slow draining. i've tried to declog the drain as best as i can with home remedies. but what other advice do you have?