How it happens

What a trap does
Holds water in a U-shaped bend to block gas from the drain system
Why it dries
Evaporation, made faster by dry Front Range air and furnace heat
Fixtures most at risk
Second bath tubs, laundry standpipes, floor drains, rarely used sinks
When it shows up
Units vacant for a few weeks, or occupied units with an unused guest bath

Why large communities run into it more

A community with two hundred doors may have a dozen vacant units at any given time, plus models and down units waiting on a renovation. Each one has several traps slowly losing water. Colorado's low humidity and winter heating speed this up compared with more humid parts of the country.

Sewer odor from a dry trap is easy to misread. Staff may suspect a broken drain line, a dead animal, or a problem in the unit below. A leasing agent may simply mark the unit as smelling bad and move on to the next tour. Five minutes with a bucket of water is often the whole fix.

Vacant unit drain routine

Add to the weekly vacant unit walk.

  • Run water in every sink, tub and shower for several seconds.
  • Pour water into the washer standpipe and any floor drains.
  • Flush each toilet once.
  • For units vacant longer than a month, add a small amount of mineral oil or a trap primer product to slow evaporation in floor drains, if your plumber approves.
  • Note any trap that is dry again after a few days; it may have a leak or a siphoning problem.

When water does not fix it

  • IfSmell returns within a day after filling trapsLook for a cracked trap, loose slip nut or a missing cleanout cap under sinks.
  • IfSmell is near the toilet baseThe wax ring or toilet flange may have failed; a plumber should pull and reset the toilet.
  • IfSmell is in the walls or ceiling, not at a fixtureSuspect a vent or drain line leak in the chase and bring in a licensed plumber.
  • IfSeveral units in the same stack smell at onceA plugged vent on the roof or a main line problem is more likely than individual traps.

Common questions

Is sewer gas dangerous?

At the low levels from a dry trap it is mainly a nuisance, but it contains gases that are harmful at high concentrations. Treat a strong or persistent smell as a plumbing repair and ventilate the unit.

Can occupied units have the same problem?

Yes, especially with a guest bath nobody uses. A note in move-in materials suggesting residents run water in unused fixtures now and then prevents many service requests.

General information for Centennial, not a quote or professional advice. In an emergency, call 911.