We just bought a home built in 1955 and we hooked up the washer drain hose to a vertical standing pipe, assuming that it is the drain for the washer. Well, as we started the washer and got to the first drain, water started gushing out of the pipe as well as backing up into the sink, filling it with some NASTY looking black sludge. Now the pipes are clogged–toilets and other sinks are fine–and I have no idea what to do. We tried plunging (but recently learned that I should have covered one drain otherwise, plunging is pointless). Any other ideas??????