I just bought my house back in June of 2008. The washing machine came with the house, and is from 2001. The washing machine started backing up at the part of the cycle when it drains the water out. The water was black and nasty, and spilled out onto the floor. I found out that the field lines in my septic tank had failed. Thousands of dollars later, we are switched to city sewer, however the washer still backs up (but the water is clean and soapy smelling- yay! :) ) The washing machine is in the basement. The main line runs down from the kitchen sink, and splits to allow the water to drain from the washer.

I have ordered the rubber washer from Sears. I realized it had a crack in it when I was examining the rubber hose that drains the water out into the pipe. I don't think that the pipe is clogged. It was snaked by the company when they first were trying to find the septic tank by running this loud grinding thing through the pipes out to the septic tank (they said that the sound would tell them where the tank was). The drains in the kitchens, bathroooms, etc, never back up and everything works fine. It's just the darn washing machine.

Do you think it could be overflowing just because of a cracked rubber washer? We have snaked the entire pipe and like I said, are completely on a city sewer now. This plumber keeps telling me he thinks there is a clog in the pipe, but if everything else works fine, and the thing has been snaked, I don't see how it's affecting the washing machine.

The cracked rubber washer would not allow it to leak that much. You should probably check the vent for that line. If the vent is restricted it will cause some major problems because there is no air flow along with the water flow. That is a very simply explnation of how the vent helps the drainage. It is one or the other. Vent or the drain line is restricted. Have the plumber find the vent for that line and make sure it is open.

Thanks for you prompt response. When you say, that the vent is not open, is that something that could just happen one day? Because for the first few months we owned the house there was no backup. Then one day it just started. Should I try snaking the kitchen sink drain? (I know, this is the "appliance" thread and I should be asking this in the "plumbing" thread, but can you give it your best shot?)

The washing machine is in the basement and I believe it is right under, and hooked to the same line as the kitchen sink. I just don't understand how the "vent" could just cease to work one day... but then again I'm not a plumber.

Usually vents do not quit working but when you have a problem like yours it is always a good idea to make sure they are open. Running a snake through the drains is a good idea since that seems to be where the problem is.

Vents are required by code.

Your house's plumbing vent's purpose is to remove sewer gases from the drainage system and equalize its atmospheric pressure. Without the vents, our toilets and all other home plumbing fixtures might not be draining properly, can cause unusual noises (like gurgling or belching as and after they discharge), and could be responsible for an unpleasant sewer gas smell inside the house.