My washing machine is next to a 2-bin wash tub in my basement and discharges into it on the rinse cycle. Lately the wash tub has been backing up. I have tried to put lint traps on the washing machine discharge hose to keep lint from going down the drain. This becomes a hassle. I recently tried Instant Power Drain Opener "Guaranteed" to work. It didn't. When I turn on my kitchen sink and let hot water run, the wash tub backs up after a few minutes and then all this "black gook" comes running out. I even found small pieces of lettuce in the sink downstairs. It stinks and won't drain! I'm assuming the piece between the trap and the vent is clogged? The house is 40 years old, but I've replaced that piece once. I've wanted to put in a garbage disposal, but was told not to because the pipes may be old and this may have some effect? Doesn't make sense to me, but maybe? I've also been told not to use powder detergent because it leaves residue in the line. This has helped some, but I still need help as to where to begin.

You have a partial blockage downstream from the basement laundry tray. To repair this problem the laundry tray vent has to be snaked out from the roof. If the laundry tray vent can't be located then run a snake down the kitchen vent.
" I recently tried Instant Power Drain Opener "Guaranteed" to work. It didn't."
They seldom do except in TV commercials.

" I've wanted to put in a garbage disposal, but was told not to because the pipes may be old and this may have some effect? Doesn't make sense to me."
But it does to me! Why would you wish to add garbage to pipes that you already have a drainage problem with? Regards Tom