This post is very correct, (except for the psi)
If a vent hose gets water logged, and runs more vertical than horizontal, it can cause a real problem in filling.
I have that problem existing in my current MH.
When it happens I use a 6" pc of hose in the vent ext fitting. and simply blow the vent line clear of water,....it doesn't take much human pressure to clear it. I always threaten to remove the (what must be) sag in the vent line, but never do.
But this still has nothing to do w/ the OP not able to draw water off a tank that is 1/3 to 1/2 full.
I would still believe there is access to an inline filter some where.
Just a caution,....don't ever put more than even 2 to 3 lbs pressure in a flat sided plastic tank,....and even that mite be too much.
Fletch Rider wrote:
I had a very similar experience. Began to occur after I had filled the tank and then towed the camper. I eventually cupped my hand around the water inlet and basically pressurized the tank until the vent line spit out water and then there was a sort of burbing and air began rushing into the vent line and all was right with the world again. I can't see the entire vent line, so the only thing I can think of is water was sloshed into the vent line while traveling and sat there until I forced it out. You could probably use air to make sure the vent is open as opposed to forcing water into the tank. But be careful not to use greater than 35 psi regardless of which approach you try or you'll have a much bigger problem on your hands.