Pure Maintenance Austin TeamQuick answer: A sour or sewer smell near a sink or shower usually comes from slimy buildup inside the drain or a dry P-trap that has lost its water seal. Clean each drain monthly and run water in every rarely used sink, tub and shower once a month. If the smell comes back within a day or two, call a plumber.
How can you tell the smell is coming from a drain?
Lean down and sniff the sink or shower drain. If you've cleaned the bathroom top to bottom and there's still a sour, musty or sewer smell, the drain is very often the source.
Drains are one of the most overlooked odor sources in a home, and most drain smells take only a few minutes a month to fix. One exception: a rotten-egg smell near a gas appliance or meter is not a drain problem. Leave the house and call your gas utility from outside.
What builds up inside a drain?
Soap, skin oil, hair, toothpaste and food. Every time you wash your hands, brush your teeth, shower or rinse a dish, a little goes down the drain, and some of it sticks to the inside of the pipe.
Over time, that sticky layer becomes biofilm: a slimy film where microbes live and grow. You may have seen it as a gray or pink slime around a drain opening or on the drain stopper. Biofilm holds on to odors, slows drains down and adds to the bio-load of your home (the microscopic particles and microbes that build up in the air, on surfaces and in the HVAC over time).
Common trouble spots:
- Bathroom sink drains and pop-up stoppers
- Shower and tub drains, where hair and soap collect
- Kitchen sinks and garbage disposals
- Washing machine standpipes
- Floor drains, where a home has them
How do you clean a smelly drain?
Once a month, clear out the hair, then flush with hot water, baking soda and white vinegar. It takes about half an hour, most of it waiting.
- Pull out what you can. Remove the sink stopper or shower drain cover and clear any hair and gunk. A cheap plastic drain snake from the hardware store works well.
- Pour hot water slowly down the drain to soften greasy buildup. Use very hot tap water or a kettle that's cooled a few minutes, not a full boil: most drains under Austin sinks are plastic, and boiling water is hard on plastic joints and porcelain.
- Add about half a cup of baking soda down the drain.
- Follow with about a cup of white vinegar. It will fizz. Cover the drain with a stopper or a wet rag and wait 15 to 30 minutes.
- Flush with more hot water.
- Scrub the stopper and drain opening with an old toothbrush and a little dish soap.
For garbage disposals, grind a few ice cubes and a lemon or orange peel, then run hot water for a minute.
Keep grease, coffee grounds and harsh drain chemicals out of your drains. Grease hardens in the pipe, and harsh chemicals are rough on older plumbing.
What is a dry P-trap?
A dry P-trap is a drain trap that has lost its water, and it's the sneakiest smell in the house. Look under any sink and you'll see a U-shaped bend in the pipe. That's the P-trap. Every tub, shower and floor drain has one too, even if you can't see it.
The P-trap holds a small amount of water. That water acts like a seal, blocking sewer gas in the drain line from coming back up into your home. As long as the trap has water in it, you won't smell a thing.
The problem starts when a drain isn't used for a while. The water in the trap slowly evaporates, especially in a warm Texas house, and the seal is gone. Sewer gas can then drift right into the room. That's why the smell so often shows up in:
- The guest bathroom no one uses
- A laundry room floor drain
- A wet bar or utility sink
- The spare shower that's become a storage spot
- A home that's been empty while you traveled or during a move
How do you fix a dry trap?
Run the water. It refills the trap and restores the seal.
- Once a month, run water in every sink, tub and shower for about 30 seconds, including guest baths and rarely used sinks.
- Flush any toilets that don't get used often.
- Pour a bucket of water into any floor drain.
- Set a phone reminder so you don't forget. First weekend of the month works well.
For a drain you almost never use, a spoonful of mineral oil poured in after the water can slow down evaporation.
When should you call a plumber?
Call a plumber when the smell or the slow drain keeps coming back. Specifically, call if:
- The smell comes back within a day or two of running water
- A drain stays slow or clogged after the monthly routine
- You hear gurgling from drains or toilets
- More than one drain backs up at the same time
- You see water under a sink or around the base of a toilet or tub
- You smell sewer gas near a wall or in the attic, not just at a drain
These can point to a cracked pipe, a bad seal, a blocked vent or a main line problem, which are plumber jobs. If there has been a leak, fix it first.
If you've had a leak or see visible growth, start with an independent state-licensed professional. We don't measure or analyze indoor air ourselves.
Freshening the whole house
Once your drains are clear and the traps are full, the rest of the house may still hold old odors in closets, corners and ductwork. A whole-home dry fog treatment from Pure Maintenance Austin can help.
We use the patented Pure Maintenance VaPURE dry fog system in two steps: a fine dry fog of a hydrogen peroxide and peracetic acid solution that breaks down into water, oxygen and vinegar, then a surface protectant. It reaches every room and closet, plus the HVAC ductwork, without getting things wet. On treated hard, non-porous surfaces it helps control odor-causing microbes and neutralizes odors, and it's done in one day.
If your AC smells musty when it kicks on, have the coil and drain line checked too. Our sister company, Gold Eagle Services, handles that work across the Austin area.
Get a free phone consultation
Want a fresher home from the drains up? Book a free phone consultation. A Comfort Advisor will call you, learn what's going on in your home and send a written quote based on square footage. We serve all of Central Texas, out to College Station (about 2.5 hours), including Round Rock, Georgetown, San Marcos, Bastrop and Marble Falls.
Call 512-904-4646 or email IAQ@goldeagleservices.com. We're open Monday through Saturday, 7am to 7pm.