2 inches pipe connection between washbasin and floor trap (main drain) has opposite slope. Washbasin has trap underneath and controls it whereas floor trap (main drain in shower) smells occasionally. The plumber says opposite slope is causing water to stay inside pipe and that smells.

Is there any way i can avoid the smell from main floor trap? Without any breakage of washroom tiles?

  • 1
    Are you actually using that shower? If not, trap eventually drying out and stinking wouldn't be very surprising, and pouring a cup or two of water into it would fix that problem.
    – keshlam
    Mar 31, 2023 at 19:34
  • 1
    The shower has a trap too, of some kind. Is the roof vent working properly? A plugged or missing roof vent can push or pull water out of the shower trap, and cause sewer gas to come up. Mar 31, 2023 at 20:32
  • Can add a bit of e.g. olive oil to float on the water and slow evaporation. Mar 31, 2023 at 22:38

2 Answers 2

  1. Pictures of the setup (edited into your original question) will help you get better answers that apply specifically to your situation.
  2. The general answer is to properly slope all drain pipes so they actually drain instead of collect stagnant water.
    • If that requires tearing up walls or floors, then that's what's required.

A temporary, band-aid solution might be run water through both effected drains daily to prevent the same water from sitting in the reverse sloped pipe and beginning to smell. Depending on your locale, it might be necessary to run water twice a day.

Again, this is a temporary, band-aid only solution that eliminates the symptoms, but not the problem. This may work for you while you plan out and buy necessary materials to DIY the work, or while waiting for a contractor to come do the work for you, whichever you choose. It is, however, impractical as a long-term solution.


To avoid the smell? Put a plug in the plughole. And/or pour bleach down the plughole periodically.

To avoid the smell permanently? Excavate to the wrongly sloping pipe, and remedy.

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