Toilet gurgle/air?

[Qwertyjjj]

The upstairs toilet is connected to the same system as the septic tank ejector pump (a bit like a sump pit).
After the pump has run, the toilet upstairs will gurgle and a big bubble of air comes up presumably through the s bend.
Also, on flushing the toilet, a big air bubble comes up and then it flushes.

Any ideas on what I can do to solve this?
The pump is vented properly so not sure what else it could be.
The fact that air bubbles on flushing is kind of strange, which means it can;t just be the pump creating a vacuum?

 

[hj]

Does your vent go out through the roof or do you have an AAV to do the venting/

 

[Sponsor]

 

[WorthFlorida]

Is this a new problem or always the bubble problem?

 

[Plumber69]

plugged pump vent?

 

[Plumber69]

bowed vent pipe full of water?

 

[Smooky]

If the check valve in the pump discharge line is not working and you have an AAV instead of a vent to the outside that would cause that problem. The same thing could happen when the toilet is flushed. The liquid going into the tank displaces the air in the tank and the air has to go somewhere.