My kitchen sink backed up. I got out the snake and unscrewed the pcv pipes below the sink and found the pcv pipes black and smelly. Why are they black and smelly, and what can I do to keep them from getting in this condition?
Thank you.

This is completely normal. Not much you can do about it other than poor some bleach down the drain periodacly, but even that will not prevent the black smellyness completely. This is one reason all fixtures are required to have vented traps, to keep the smell from entering the home. Kitchen sink drains are usually a bit worse than other drains because of the food that goes down them. Just the way it is, wish I had a better answer for you.

Thanks 77,
I won't put bleach down the drain because we're on a septic system and it'll kill the 'good' bacteria in the tank. Instead, I'll try yeast and see how that works. I'm told yeast likes smelly bacteria and will eat it and leave a nonsmelly waste behind. Thanks again.

Skip the yeast and don't worry too much about bleach unless you were thinking of using many gallons. All drain pipes get smelly and blacken with slim, totally normal.

Thanks 1,
The snake worked fine, but I believe it only punched a small hole in the clog, enough to let the sink drain but not drain as fast as it once did. I'm in the market for a better snake, because I feel this won't be the last of cloged drains.

Why are the insides of my kitchen pipes black and smelly?
Built up grease and rotting garbage from your disposal is what you see and smell. A little bleach isn't going to destroy your septic system, At night before bedtime pour a quart of bleach down the drain and let it set.
Next morning flush the mess out with a few pans of boiling water.
Good luck, Tom

Thanks SB,
I'll give that a try after all. I should have mentioned I didn't smell nor see anything until AFTER I uncoupled the pcv pipes below the sink. It was then I noticed the blackness and the smell.
Are there any commercial compounds that 'eat' clogs overnight or over several days and nights? I've thought of pouring a few cans of Coke down the drain, knowing what Coke does to a nail left overnight... it just eats it up. Maybe it'll do the same to a clog?? Or maybe battery acid?
(just kidding!) Thanks again!