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Question DetailsAsked on 11/21/2015

water backs up into bathroom sink

The drain pipe for our downstairs bathroom is connected to the drainpipe for the utility sink prior to going into the sewer drain. The pipe is at an angle so there is downward drainage. Every time the utility sink fills with water it backs up into the bathroom sink. There doesn't seem to be a clog in the drain pipe because it does drain into sewer drain.

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1 Answer


If the downstairs bathroom backs up ONLY when the utility sink is draining, but NOT when upstairs water uses (especially toilets or emptying tub) are draining, then you have a partial clog in the pipe between (or at) the wye where the downstairs bathroom and the utility tub come together, and the wye where that pipe meets the main sewer stack. This could almost certainly be cleaned out with a snake by a Plumber.

One other possibility if this has always been this way, if that pipe is undersized. By most area's codes should be minimum 1-1/2 (old code) to 2" (current code) from the utility sink and minimum 2 inch to the wye where it meets the bathroom line, then 3" minimum from there, and with some high-flow modern washers, 2" or larger instead of 1-1/2" from standpipe to the junction depending on slope and number of turns.


However, if backup (or gurgling in the bathroom) occurs when any OTHER source of water (from upstairs) is draining, then your partial blockage is in the main stack downstream of where the combined downstairs pipe comes into the main sewer pipe. This might be cleared with a snake, but I recommend in this case (especially if this has not been done in the past 10 yers or so) that you get a Sewer and Drain cleaning company to run a full-diameter scraper head router past that point all the way to the street, to clear any clog and also to remove built up grease and fibers that reduce the pipe inside diameter over time. Doing this not only restores the pipe diameter, but also chases the clog all the way to the main sewer (or septic tank) rather than just punching a hole through the clog or pushing it ahead to create another blockage point in a few days, as a snake cann do.

Answered 5 years ago by LCD

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