Pumpout suction sucks bowl empty

[paul712]

As the title says, when I get pumped out the suction is enough to pull open the flapper in the bottom of the bowl and suck the contents out. I never gave this much thought, in fact I kinda didn't mind because I fill the bowl up with water right before a pumpout to give the lines a good sucking.

The toilet is a Jabsco 37010 electric, ancient, works great, raw water, noisy as hell, flushed moderate amounts of paper and solids for years, never any clogging issues and only odor issues are if there are too many burritos in the tank.

I'm a huge fan of leave well enough alone, especially when it comes to toilets, but now I'm curious. Is it “normal" for a pumpout to suck the bowl empty?

 

[rommer]

Sounds like your holding tank vent line is clogged. Try back flushing it with a garden hose. (Make sure you don't have a vent line filter first, getting that wet will cause a blockage)

 

[paul712]

I wondered that but it's definitely not clogged. It could be too small to equalize against the pumpout machine though, that bad boy seems to suck pretty hard.

The system works great, but I do wonder if this is normal.

 

[Vic Willman]

That's what happpens when your holding tank vent line is either plugged up, or isn't large enough in diameter.