For those whose RV is connected to a drain most of the time, you probably keep your gray water valve open. At times a smelly little problem arises: Sewer gases can come back up the sewer hose, into your gray tank, and slow migrate their way up the through the tank and out the roof vent. At times those same evil essences can somehow re-infiltrate your RV with a negative impact on your olfactory organs.
Worse still, if there are any “vague” connections in your gray water venting system, those nasty little essences can also make their creeping way out, carrying not just the odor of gray water (as bad as that is) but with a direct connection to the city sewer (or local septic system) that REALLY horrific scent of black water can invade your premises.
What to do? Enter the Folgers P-Trap solution: If you leave your sewer hose connected and the dump valve open, stick a P-trap between the sewer and you. Simply obtain a coffee can (or a large rock, and make a bend in your sewer hose, as illustrated in the photo here. Gray water will advance over the bend, but the water trapped in the hose on the “rig side” of the coffee can will prevent the odoriferous fumes from crossing over.
Mind you, when you dump your black water you’ll want to temporarily remove the coffee can to allow a free-flow of black water, etal, to make the trip down the sewer unimpeded.
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I think that keeping the gray valve open all the time is a poor idea. Allowing the gray tank to fill ensures that the tiny solids it contains are flushed out when it drains instead of accumulating on the bottom of the tank, and, more importantly, a full gray tank provides flushing water after a black tank dump.
I agree….Leaving it open is a bad idea.
I leave the gray water open if we are camped for ten days or more and using the washer. Then I close it a day or so before I empty the black water. This allows the gray water to fill up and to flush out both the gray water tank and the hose after the black water.
Too many RV Parks already solve this problem by expecting your sewer water to run uphill. The Sewer connection is higher than the outlet from the RV. I have no idea what the “engineer” is thinking when he/she set up RV sewer connections.
I leave gray valve open, we are staying in a cmap ground for severl months. The wife does dishs 1 or2 times a day plus we take tow or three showers a day, that should be enough water to keep the tank flushed out. And for the black tank I have Sewer Solutions macerator which uses water while dumping black tank, so I do not need gray tank to flush black tank.