Gray water at a glance
- What goes in
- Sink and shower water, soap, grease, food particles, hair
- Typical smell
- Sour, rotten or swampy, sometimes like spoiled milk
- Main escape routes
- Dry P-traps, air admittance valves, shower drains
- Worst conditions
- Warm weather, partly full tank sitting for days
- Common mistake
- Treating only the black tank and ignoring gray
Why gray water smells
Gray water looks harmless, but it carries organic material. Dish water brings grease and food bits, the shower brings skin oils and hair, and all of it settles in a tank that is rarely rinsed as carefully as the black tank. Bacteria break that material down, and in a warm tank the process produces sulfur-smelling gases quickly.
Each sink and the shower in most RVs has a P-trap that holds water as a seal. On a long drive, sloshing can empty a shallow trap, and in storage the water evaporates. Many rigs also use air admittance valves under the sinks instead of running every drain to a roof vent. These one-way valves let air in so drains flow, then close to keep odor out. When the internal seal sticks open or fails, tank air leaks straight into the cabinet.
Colorado's dry air works against you here. Traps evaporate faster than in humid climates, so a rig parked for a few weeks between trips can have open drains by the time you come back.
Gray odor checks under the sink and shower
- Run water into every drain for several seconds to refill the traps
- Open the cabinet under each sink and smell the air admittance valve area
- Look for a slow drip or film around trap slip nuts
- Check that the shower drain trap is not cracked or loose
- Smell the outside gray valve and termination for leaks
- Note whether the smell gets worse after dumping or before
Clearing a smelly gray system
Scrape and wipe dishes first
Keep food and grease out of the drain. Wiping pans with a paper towel before washing makes a large difference over a week of camping.
Dump and flush on a schedule
Avoid leaving a partly full gray tank sitting for days in summer. Dump after the black tank so the hose is rinsed with gray water, then flush the gray tank with clean water if your rig allows it.
Replace a suspect valve
Air admittance valves are inexpensive parts on most rigs. If odor comes from the cabinet and the traps are full, swapping the valve is often the fix.
Clean the cabinets
Once the source is closed, wash the cabinet floor and walls. Particleboard under sinks absorbs odor if it has been wet, and swollen sections may need replacing.
General information for the Denver area, not a quote or professional advice. In an emergency, call 911.