[porthole]

Grey tank valves left open - a bit of controversy.

Allegedly modern sewer systems in CG’s are designed to be a closed system, eg not vented throughout the campground via trailer plumbing.

Aside from that, one of the joys of leaving the grey open is when your neighbors dump their tanks. That open grey valve is a direct vent to the roof and is probably why full hook up campgrounds stink on Sunday morning.

With 75 gallons I don’t see a reason to leave it open. But, if I have to leave the rig for a period of time and I’m not sure of the spousal intents, I will leave the grey just cracked open a bit. Letting the water trickle out.