A little while ago, our plug stopper cross bar that is built in the drain broke loose & ( I assume went down) the pipe. Oh shoot!! So I began the waiting game for the plug up. Actually it's been about 1 yr. Since then we got a plug & plungered up a butter knife!! It looked like a brown turd shooting up out of the drain when we pulled off the plunger!! Hubby plunged & I grabbed & we got it. 9 mos. later now I got a stopped up kitchen sink! No draino or anything else sitting 3 days(what a pain doing dishes in the bath tub!) removed this thing! We snaked the sink as far as it would go,went with the snake down thru the roof vent into the tank to get the rest of the pipe. What in the world is the problem? Figured out it was a $3.00 vent trap @ home depot! Thank you god! Cutting out pipe in this '87 would have been a major undertakeing I would rather have cut off my left arm instead of doing!!! The first two morons (depot floor associates) we talked to had never seen such a thing. Knowing it was a pvc Home Depot item we got a mgr. & he said "oh ya "they're right here." 4 days of bliss!! Then... it backed up again!! The elbows, twists,turns & all told me it was not another "turd". So I think it had to be that darn drainstopper thing built in the drain in ther somewhere reaking havak! How I don't know since we snaked it clean already to the holding tank?? I haven't lost any rings so what it was I can't imagine,but the snake (yes try,try again)hit a snag going down thru the roof vent which is a straight 10 ft. once you hit main line to the tank. With 250 lbs behind the snake & some serious determination we pushed it thru. My pipes are clean enough to eat off of & I'm going to tell you what did it. Sulpheric acid. I was @ wits end & going to use muratic acid before cutting pipes but found this stuff @ the "depot" & used it & the snake even going into the tank & thrashing around came out CLEAN!!!!!!! It's $12.00 a half gallon. Not even an odor on it!!! Beats the cascade out! It's in the plumbing dept. & I'm sorry I threw out the jug but it's the only black one & just read the label. Hope this helps someone.