Our house was built on slab in 1969. It was a rental for several years before we bought it and Lord only knows what the tenants poured down the kitchen sink (fry oil and rice? Motor oil and feathers?). Anyway, the laundry room is at the very beginning of the drain line. From the laundry room, it goes to the kitchen, the guest bath, the master bath, and then out to the main line. When we just use the kitchen sink (double sink with a disposal) or the dishwasher, we have no problems. When the clothes washer drains, it backs up a couple of inches into both sides of the kitchen sink. There are no problems in either of the bathrooms.

I got up on the roof and ran a snake down the vent line, and when I brought the snake back up it was covered with what looked like tar. Oh, did it smell delightful!

On the recommendation of a plumber that I trust and have worked with in the past, I poured a bunch of foaming pipe snake down the drain. He said that the black goo I brought up with the snake was "pipe plaque" and it was pretty common in older houses. It helped a bit, but now I get one or two inches of water in the kitchen sink instead of three. Hooray! I have also tried the baking soda and vinegar trick and didn't see any results. Ditto for the drain enzymes and lye.

I'd prefer to not dump a bunch of chemicals down the drain, but I'm kind of at a loss. Reading through the posts, I'm guessing that the "plaque" is made up of grease and cloth fibers. Should I rent a power auger from Home Depot and have another go at the vent?

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Should I rent a power auger from Home Depot and have another go at the vent?

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That's what I would do. The blockage is downstream from the kitchen so that's the vent to snake. Use a auger tip first and then change to a cutter tip(see images) to clear the pipe wealls of the grease and fiber build up. Put out enough cable to reach the base and 16 feet more. Flush with hot water. Good luck, Tom

Thanks! I'll give it a go on Wednesday.

Tom is right, none of us advocate chemicals for trying to clean 'Plaque." Once in a blue moon someone might consider chemicals if the clog were in a closed trap or running trap, the chemicals can sit and soak. Soaking will not happen in a slow drain so take the cutter snake approach and flush with plenty of hot water when you are done.