I moved into a new home with laundry room in basement and started to notice occasional wafting of sewer gas out of the laundry drain pipe. It is an older home built ‘58. It looks like there is no p-trap. How could this be? How should I correct it?

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  • Please add more photos including washing machine drain connection, where smells are coming from, and what pipes we are seeing in the photos. Also, is the brown tile a floor or the wall?
    – Armand
    Mar 22, 2023 at 1:52
  • Brown tile is floor
    – user164651
    Mar 22, 2023 at 2:07
  • Photos added - odor comes out where the drain tube for washer goes in
    – user164651
    Mar 22, 2023 at 2:14
  • Could you post lower-down views of the area where the two white pipes connect to the cast iron? Also, does the horizontal white pipe drain or connect to anything other than the vertical pipe with air admittance vent on top?
    – Armand
    Mar 22, 2023 at 3:45
  • In general, I think adding a p trap above the current area where the white pipes join should do the trick, but you have to be careful to avoid a setup that will act as a siphon and not leave any water in the trap. Perhaps a trap on the horizontal pipe and the standpipe shifted over to feed into it? The actual plumbing experts here should have solid advice for you.
    – Armand
    Mar 22, 2023 at 4:01

2 Answers 2


You should investigate if the old cast iron pipe has a trap of some sort below the brown tile floor (if there is a basement or crawl space below this floor). In all likelihood there is not such trap present but checking makes sense in case there is some type of failure there.

Since the existing merge of the white PVC pipes to the cast iron piping (via the few shown black fittings) is so close to the floor you may be faced with having to replace some of this white PVC piping. It is probably going to require adding two separate P-Traps, one for the vertical line feed from the washer drain stand pipe and a separate one in line with the horizontal section that currently feeds into the stand pipe. There just does not look like there is room to place a trap below the horizontal to stand pipe Tee.

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For comparison/reference:enter image description here

Not ideal, but it does illustrate the idea: replace the current direct drain with a horizontal, a trap, and then the required length of vertical pipe.

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