Q: My washing machine is located in the basement in a room directly beneath the kitchen. When water drains from the washer, it’s going into a hole in the basement floor. The sump pump kicks on, but the water comes back up into the kitchen sink.
The water recedes, but I’m not exactly sure to where. Anytime any water enters the sump hole, the pump kicks on and water comes back up into the sink — this could be water draining from doing dishes in the sink or even just accumulated condensation from the A/C or from the high efficiency furnace. Could this be caused by the vent pipe on the roof being clogged?
A: I have often seen the arrangement you describe with a basement laundry located under a kitchen. In most cases the main sewer drain is located halfway up on the basement wall near the laundry equipment.
The kitchen drain enters the main sewer pipe near where the sump pump drains into the same pipe, or the two drainpipes are connected together at that point. When the sump pump comes on, it forces water into the main sewer faster than the sewer can drain it away, so some of the water is forced up and into the kitchen sink. When the pump stops, the water from the sink slowly drains back through the sewer.
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Most likely the main sewer pipe is clogged or is damaged and that’s why it cannot drain quickly. Have a plumber scope the sewer pipe with a camera to check for damage or blockage. Older clay sewer pipes attract tree and plant roots that can be removed by the plumber. A damaged or broken sewer pipe will need to be excavated and the damaged sections replaced. If the two drain lines are connected together at the sewer, have the plumber inspect the two drain connections and rearrange them if necessary. If the plumbing vent were blocked, the sewer would still drain quickly when the sump pump came on and the kitchen sink could become the vent. You might even hear it gurgling as air was pulled into the drains.