I am replacing the old washing machine drain stand pipe, p-trap and clean-out. I am adding a utility sink to the garage laundry area washing machine vent stack.

Am I creating a possible issue by placing a new 2" san-tee (which will reduce to a 1.5" union p-trap for the utility sink) just below the 2" san-tee that leads to the washing machine p-trap.

Washing machine p-trap is welded, 2", 18" from floor, stand pipe is about 20" with a total height of about 38" from floor (top of washing machine is also 38", machine has a 41" drain hose)

This is a remodel of a 50 year old condo, not being inspected.

First image is the as-built that is being replaced

As built

New work

New work


1 Answer 1


A clothes washer is 2 DFUs (residential) or 3 (commercial,) per IPC code (may not be your code, likely to not be THAT different, though.)

A "service sink" (which I take to be what they call a utility sink) or "Laundry Tray" (another possible meaning) are both rated at 2 DFUs

So you have 4 or 5 DFUs total, on a dry vent that can handle 12-20 DFUs depending on length.

No need to change it, no problem.

The 2" drain, properly installed, can handle 21 DFUs, so also no problem.

  • Thank you for the answer. The more I learn about plumbing, the more I realize it's easy for a DIY'r to introduce very subtle issues.
    – Richard
    Aug 3, 2022 at 17:10
  • 1
    Indeed. The "plumbing I learned from the way the house I grew up in was built" is horribly outdated, and has caused me to chop holes in a concrete floor to fix things once already.
    – Ecnerwal
    Aug 3, 2022 at 17:13

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