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**a64pilot** · 25-11-2019, 06:19

A clogged vent would push both waste and air back into the head, as of course there is pressure and it would push that until it equalized.
But a clogged vent is easy to verify, simply go to direct discharge and if it still bubbles back it’s not the vent, cause your not connected to the tank anymore, you have bypassed the vent too.
Or of course verify it’s not clogged like Sailor boy did. On my old 5/8” fuel tank vent that was also used as the waste tank vent a garden hose would fit over it and you could easily tell if it was clogged or not. Mine clogged once from dirt dobbers which is some kind of wasp that lives down South and makes its nest from mud and loves small holes.

I believe the reason mine pushes air back when the joker is slightly open is two fold, one it’s because my electric head pumps quite a bit of air into the hose at the end of a flush, which I think is good cause it flushes out the hose well. Secondly I believe air will leak due to first it’s viscosity and secondly due to its lack of mass, air will leak though but water will force the lips of the Joker closed, as it’s sort of a reed valve

sailorboy1 · 25-11-2019, 06:25

So ................................. I "fixed" it:

I was about to pull out the mattress and take it's base off as that covers the holding tank so I could get to the vent connection. This is a big PITA so I figured I would try the "blow water back down the vent line" again first. But this time I took off the deck pump out cap first. Well that really resulted in blowing the vent out and once the water started flowing it pressurized the holding tank enough that it was back flowing all the way up to the deck pump out fitting.

So lesson learned is to flush out the vent line you need to take the pump out cap off. This seen obvious ..................................... NOW!

**a64pilot** · 25-11-2019, 06:37

Glad that it was an easy fix

CaptTom · 25-11-2019, 06:50

All this talk about flushing the vent line with water makes me nervous.

Sure, it should work, in an ideal world. And apparently it worked for Sailorboy.

In some cases, however, vent lines can develop a sag along their length. There can be hidden filters in-line left over from a previous owner or even the factory.

In either case, you don't want water in vent line.

sailorboy1 · 25-11-2019, 09:19

That seems excessive paranoia.

CaptTom · 25-11-2019, 11:06

Quote:

Originally Posted by sailorboy1

That seems excessive paranoia.

Maybe it's just laziness

At any rate, I've had vent lines plugged up, both by waste and by water. So it's something I try to avoid. I don't let it rise to the level of paranoia though. And if it works for you, keep doing it!