I have a secondary plumbing stack in my home that has the kitchen sink attached on the main floor and the washing machine in the basement. This stack is vented through the roof of the home. If the sink is filled on the main floor and then the drain is opened, the water flows quickly out of the drain then will proceed to back up and overflow the washing machine stand-pipe. The washing machine draining does not back up. I snaked the line to about 20 feet and found no obstructions. What should my next mode of attack be?
Thank you in advance.



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Snake further than 20', or use a heavy duty power drain cleaning machine.
There is a blockage of some sort in the piping.

High efficiency washer, or an old style top loader? (just for curiosity sake) You need a professional auger or hire someone to use one. If you are using a 1/4 snake on a drill or hand crank you are probably actually getting about 7' into line. When a cable is in the line it spirals around the pipe slightly until it hits a blockage, then it really corkscrews around. The cables are made of heat treated spring steel, so as they coil, they build power until the head penetrates the blockage and spins violently as it releases the spring tension it was building up and basically acts like a blender. 1/4 cables don't have the tension to build up this power and just coil up until they are in knots if they get to the blockage at all. If the cable itself isn't a professional quality cable, it is even worse; grandma's knitting has as good of a chance.

It's a high efficient washer. It doesn't overflow when it's draining. The drain auger I used was just a cheap one from a hardware store.thanks for the advice.

The high E machines don't dump much water and so the pipe never fills to overflowing.