What's making a stink in your sink? It may be your P-trap

As warm weather and vacation season near, ensure that water evaporation isn't breaking the seal under your sinks and tubs.

By Tony at MSN Real Estate Feb 29, 2012 11:47AM

© Steve Wisbauer/Getty ImagesMost of us don't live in a sewer.


But sometimes, when we return home after a long vacation, our ground-floor bathroom inexplicably smells like one.


Or we find that all the air fresheners in the world cannot cover the unpleasant odors in our vacant investment property.

One solution: Check your P-trap.


Post continues below

You may know the P-trap as the curvy bit of pipe under your sink. Below the drain, you'll notice that the plumbing often forms a half-loop, before heading out at a 90-degree angle.


When this bend is filled with water — as it should be — it forms a seal, helping to stop anything from the other end of your drain-vent-system from coming up the other way. Just like that, your sink or tub is protected from nasty, noxious sewer gases floating through your plumbing and into your living space.


U.S. plumbing codes require P-traps in every drain opening. The codes also specify the proper angles and materials for the traps; they can differ in other countries.

Over time, however, the water inside P-traps can evaporate, breaking the seal and allowing these fumes to stink up your place — or, in extreme cases, explode.


As we near warmer months and may plan to leave town for an extended spring break, it may be wise to run the bathroom sink a bit before any long absence. It could be a task for whoever is watering your plants or looking after your place while you're gone.

Popular Mechanics recommends pouring boiling water down these drains weekly, to prevent clogs, as well.


A trap primer, which adds water to traps that don't see regular use — think basement or garage drains — also could be an option.

The P-trap gets its name from its shape, which also resembles a J. And just in case your mind wandered in this direction: Toilets typically do not have P-traps. If you suspect there is a septic-system odor emanating from your toilet, it could be coming from an improperly installed toilet flange, which mounts your toilet to the floor, or a leak in the wax ring that seals the flange to the toilet bowl.


— Tony Stasiek is a producer/editor at MSN Real Estate.




Jun 9, 2012 4:27PM
If it is a bathroom sink sometimes you get a smell from the overflow on the sink itself if it has one. Another problem is if you have a mechanical vent or pro vent under the sink sometimes the spring weakens or the rubber seal lets go allowing sewer gases to come in. Ive had an instance on a job where a vanity had been relocated, whoever moved it did not cap off the pipe at the old location in the wall. It took years for the smell to permeate the sheetrock and contaminate the room. Most toilets have traps incorporated into them, thats what holds the H2O level in the bowl. Yes the toilet wax seal could be gone. There are certain types of insects that actually eat the wax over time. Put your nose to the floor where the toilet bowl meets it and sniff. If the toilet bowl bolts are loose and the toilet wiggles on the floor chances are for sure the wax ring is over compressed. If you have a plugged  roof vent sometimes water can syphon out of the toilet when flushed especially if another bathroom is located above. Squirrels have a habit of dumping acorns down vents. I've also come across homes where someone has installed a drum trap upside down preventing a water seal. If you live in cold climates and leave for extended periods pour non tox antifreeze into all your traps. Shut H2O supplies off to toilets flush them and pour antifreeze into bowls and tanks. On disposals every so often grind up a handfull of ice cubes to clean blades. They have special foaming cleansers made specifically for disposals.
Jun 9, 2012 4:16PM
Try your disposal unit if everything esle has failed. If you have an old unit they will start to stink after a while. Try using some disposal beads or disposal odor eliminator. if this does not work, try changing the P trap and/or Disposal Unit
Jun 9, 2012 3:18PM
we have changed the Ptrap and still get the smell.  The sink is used daily.  Any ideas what else it might be? 
Jun 9, 2012 3:11PM
Wish we could afford to go away on a vacation long enough for the water to evaporate in our P-traps :-((

As for leaving your home unattended for a period of time, my suggestion would be to turn off the main water supply to the house and the gas or electric to your water heater.  If you live in a cold climate then also drain the pipes, the water heater, plus (after the main is turned off), flush all the toilet bowls.  This way if the heat fails while you are away, there is nothing that can freeze hard and crack.

Now for folks who have steam heat, I would suggest you call your plumber.  Years ago my grandmother's oil fired steam furnace failed in the dead of winter while she was away on a work assignment and the steam radiators and supply pipes froze hard and literally exploded.  The flying metal punched holes in the walls and ceiling, not to mention the water damage.

Jun 9, 2012 1:25PM
Another place to check is the drain from the air conditioning condensate pan. This is something most people never look at very often. There is usually a pipe or hose that takes the condensation water from the pan to a drain close by. The drain may be shared with a pipe from the pop-off valve from a water heater. Typically during the winter the A/C unit doesn't run which then doesn't drip condensation water to the drain. The trap for this drain will dry out and you may start getting a bad odor that sometimes is hard to find depending on where your unit and drain are in the house or garage. Here in Oklahoma I start getting a whiff of this smell in late February. I pour 2 cups of water into the drain and maybe a 1/2 cup of scented bleach too. That usually takes care of the odor until the A/C kicks on in April or May.
Jun 9, 2012 6:44AM
The p trap is built into the toilet bowl. So yes,,, a toilet does have a P trap.,,,, just not one under it.
Jun 9, 2012 5:36AM
  I make it a habit to pour a cup of drain cleaner into every drain in the house every two weeks as a preventative. Never had a clogged drain.
Jun 9, 2012 5:27AM

I am a plumber also I always incourage shutting your main water valve off if you are leaving your home for a period of time like even a long weekend I have been to too many houses up here in MN in the winter that the heating sytem quit while they were gone and a water pipe froze and split and then flooded the house. I was at a townhouse that had 42 different splits in the piping through out the house. try using Rv anti freeze in those drains that is how we winterize every house.


Jun 9, 2012 4:46AM
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Jun 9, 2012 4:32AM
If you are going on vacation just close off the drain the very same way you do when you keep want to keep water in the fixture. Sometimes it will not matter what you do as the piping may be installed wrong. Most states use national code which requires venting. If there is no air vent whether it be mechanical or piping you will have siphoning of the p trap as it is now a full s trap without the vent. Call a reputable Plumber to check it out.
Jun 9, 2012 12:26AM
i take a shop vac and clean them out and then put in new water bad smell it dose get better
Jun 8, 2012 10:16PM
A tablespoon of vegetable oil added to the p-trap will slow the evaporation of the water.
May 12, 2012 4:49PM
I'm a Plumber. One trick is, when your planning an extended vacation, open your sink and tub faucets till you see a couple of drops a minute. Doesn't have to be much, maybe a drop every 20-30  seconds should do. This will keep a constant source of water to the p-traps, keeping the traps sealed and sewer gases out while your away. Beats having to pay a house sitter which most of us can't afford in the first place while the cost of the water used for this purpose is pennies.
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