Regarding traps.
When working as they should, a trap will block the flow of gasses from a holding tank. But things don't always work as they should. Among other things, winds blowing across a vent can push or suck water out of a trap. This can happen when parked or towing. Colorado is notoriously windy in the mountains, and the vents on the sidewall of a PUP are typically only inches above the traps. The photo depicts the vent for the shower in my old PUP. A hardside may be vented through the roof, but there is little to prevent a wind pressure wave from pushing water out of the trap.
I have a floor drain at home and a little-used bathtub in the spare bathroom whose traps must both must be filled regularly, or the trap dries out and allows sewer gas to escape. The same is true for RVs. When parked for several weeks, there is nothing to stop the trap from drying out and allowing the stench from the grey tank to enter the coach.
Most coaches have at least three grey water traps: kitchen sink, bath sink, bathtub/shower. After towing and setup, it's wise to run a bit of water into each trap to ensure they are full, and then monitor them in windy conditions.
Having established that traps are not foolproof, bear in mind that, if you run your grey tank open to the RV park's sewer continuously, if a trap runs dry, you won't just admit grey tank stench. It will be sewer stench. Not to mention that particulates in the grey water can precipitate out, collect on the bottom of the grey tank, and dry there if there's only the occasional trickle from a faucet to flush them away. When you're done with breakfast dishes, you may go off on a hike and not return until dinner...meaning no water down any drain for hours. Keep the grey tank dump valve closed except when dumping.
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Jim & Renee
2020 Jayco Jay Feather X-213
previously 2014 Forest River/Rockwood HW 277
2006 Ram 1500 4WD Crew with Firestone Airbags
Every weekend boondocking in the National Forests or at Lake Vallecito.
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