What Size PVC Pipe for Sewer Drains


  • A standard rule of thumb is that sewer pipes leading away from a toilet are 3 inches in diameter. Sewer drains from laundry sinks or washing machines are 2 inches in diameter and those from sinks in the kitchen, bathroom or powder room generally use a 1.5-inch pipe. The main sewer pipe leading to the septic tank or public sewer is usually 4 inches. It is important to look to the local plumbing code to see if it varies from these standards.


  • Some people think they can decrease the likelihood of clogs by using larger pipes. This can be a mistake. The water pressure helps solid wastes move through the pipe and large pipes spread that pressure out. So a larger pipe may slow the flow of the drain water and cause waste to pool.

Expert Insight

  • Tim Carter of Ask the Builder recommends a 2-inch sewer drain on a bathtub just as most plumbing codes require on showers. Although code may allow you to get away with a 1.5-inch drain, a 2-inch pipe better accommodates a plumber's snake and prevents clogs from hair.

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