Anatomy of a DIY Fail: Why Your New Sink Leaks Only When the Dishwasher Runs

One of the most confusing DIY sink failures happens when everything looks fine—until the dishwasher runs. Then, suddenly, water appears under the sink. This isn’t random. It’s the result of a complex plumbing intersection that many homeowners don’t realize exists.

Dishwashers don’t drain the same way sinks do. They rely on high-loop hoses, air gaps, or disposal inlets to prevent backflow. If any of these components are misaligned or improperly connected, water is forced into places it shouldn’t go.

Garbage disposals add another layer. Forgetting to remove the knockout plug, misaligning the discharge tube, or mismatching drain heights can all cause water to back up only under pressure—like during a dishwasher drain cycle.

Because the leak doesn’t occur during normal sink use, it’s often misdiagnosed. Homeowners re-tighten fittings or reseal the sink, missing the real cause entirely.

At I Hate My Sink, we approach leaks like systems problems, not surface issues. When water only appears during dishwasher use, it’s a signal that the plumbing anatomy needs expert attention.

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