Holding tank odors invading? It may not be your black water system

After a long day behind the wheel, you're more than happy to pull to a stop, set the brakes, and ready to make camp. How about a cold drink before setting up? You whip open the trailer door and – the stench is enough to knock you over. What's the matter, did you forget the toilet deodorant? Just because there's a stink doesn't necessarily mean the blame falls on your biffy.

When your RV plumbing system smells, the black water system often gets the finger pointing. But there are other suspects that may need an interview. Sometimes that horrific odor comes from the gray water system. A bit of detective work can help you track down the stinker.

The toilet system is pretty straight-forward. You have only a few things to check out. First, put water in the toilet bowl and let it stand. After a while, check it. The water level should not have changed in the toilet bowl. If it's gone down, then you've got a leaky bowl seal or sealing mechanism that needs attention.

Absent a leaky bowl seal, the next possibility is the floor flange gasket. These little rubber guys form an air-tight seal (in principle anyway) between the base of the toilet and the floor. If that gasket is compromised, either by age or by the toilet flange bolts not being tight enough, then air-to-air transfer can waft a nasty odor into your rig. First check flange bolt tightness: Your toilet should be tight to the floor, not "wiggly."

Before condemning the flange seal or gasket, make sure the gray water system isn't passing gas and pointing the finger at the toilet. Here's where your sniffer will be pressed into service. When you enter your RV and detect the stink, be brave: Shut the door behind you and carefully walk around sniffing. Your objective is to find the highest level of stink.

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The gray water system has several points where odor can migrate up into the coach. Sinks and shower drains should all be equipped with P-traps, that when filled with water, prevent the upward migration of odor. If the P-trap should dry up, the stink will easily encroach on the coach. If you're in hot weather and perhaps haven't used a sink or the shower in a while, the P-trap could be empty. Just pour a little water down the drain.

Another source of gray water stink is a defective air admittance valve. You'll often find these in the same cabinet as a sink; the device sits atop the drain system and opens to admit air when water runs down the drain, breaking any vacuum, and allowing water to run down the drain quickly. However, these valves are known to go whacky and stay "open" even when water isn't running down the drain, thereby allowing gray water odors to pass back up into the coach. If your nose detects stinkeroo under the sinkeroo, yank the offending valve loose and replace it – they're an inexpensive part available wherever plumbing supplies are sold.

If your RV is equipped with a washing machine (or is set up to accept one), you may find that where the machine drain hose attaches to the RV drain system that the P-trap you'd expect just isn't there. It's a weird world, but many RVers report that after they've had a washer professionally installed they've suffered stink issues, only to find the installers didn't put in a P-trap. We're not sure of the reasoning, but it's probably spelled P-R-O-F-I-T, but some outfits just don't put in a P-trap. And if the drain hose from the washer isn't then air-tight sealed to the gray water system, stink will follow.

Checked out the usual suspects and the stink remains? OK, pull the toilet up and replace the flange seal. If that still doesn't kill the odors, you may have a plumbing line in the rig that's not completely sealed. That's a tough one to track down, and may require a sensitive nose and persistence to track down.

Meantime, here's a few other ideas that can help: Use sink strainers, preferably wire mesh ones, to keep food particles from running down the drain. Try an enzyme or bacteria based holding tank treatment in the gray water system, and avoid bleach-containing dish detergents.