[TJ Clark]

When the grey water bypass is not engaged. As in I don't have the sewer hose connected and the bypass is not open. My toilet spits back when flushed. 
Lots of air comes back into the bowl when the flapper is opened. 

It's like the chamber below the toilet is pressurized before the waste is allowed into the chamber. The air that is forced up through the bowl is also very smelly, no matter what was in the bowl before flushing.


This is not happening 100% of the time. But 100% of the time that I have the hose connected and the bypass valve open it never happens. 

Do you think I have a clogged vent? Should I run a snake down from the roof? 

Is it something else?

[Richard]

What air pressure are you running on the toilet?

When is the last time the sequencing valve was serviced or lubed? Cause it sounds like the sequence of events is a little off.

I pour a bit of Mr Clean or Lysol in the potties once a week. It cuts down on the smell. I think the hopper gets funky.

[TJ Clark]

I have not adjusted anything on the sequencing valve. Mostly because it functions normally with the bypass open allowing the grey to exit.

[Georgeb]

We had the same problem. It was the valve.