Will a seldom used trap dry up?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by MushCreek, May 18, 2013.

  1. MushCreek

    MushCreek New Member

    Apr 30, 2013
    Travelers Rest SC
    In our new house, I am building a basement bathroom which will only see light use. I'm putting in a bath tub because I feel there should be one in the house. The master bath only has a shower. The tub may NEVER get used. At the least, it could go a year or better without use. Can the trap dry out from sitting that long? How would you prevent this? Would a plug work, or will it eventually dry out from the other side? Or should I schedule running water in it periodically, like changing smoke detector batteries?
  2. DougB

    DougB Member

    Jun 19, 2010
    Software Developer / Engineer
    Minneapolis - Land of 10,000 taxes
    The water in the trap will eventually evaporate. After the trap is filled with water, add some mineral oil. It will float on top of the water and will not evaporate.
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  4. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona
    The trap is exposed to air on BOTH sides of the "J" bend, so mineral oil on the "inlet" will not prevent evaporation on the outlet side. Pour recreational vehicle antifreeze into the drain, and replace it anytime you flush water into the tub. A trap will go dry in a matter of weeks, not months or years, if not used.
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