Hi! My approach would be to test the vacuum when the pump is attached to the tank! I have a spare 90 deg hose fitting, as unless you’re replacing the hose from the funnel (the old hose is almost impossible to remove off the bend), a spare 90 deg bend makes troubleshooting easier. You can either use the vacuum gauge in the hose bend end or a rubber squash ball works great to hold the vacuum! Start the pump, let the vacuum switch stop it and see how long it holds vacuum.
This approach tests the complete unit including the vacuum switch, duckbills, bellows, O rings, and 90 deg bend seal!
One of my units started kicking on recently every 10 mins or so, but water was staying in the bowl, so the seal was good! Testing the complete pump/tank assembly as described above, the vacuum held overnight, so that meant the leak was either the pedal cartridge shaft (o rings) the funnel or hose. The shaft cartridge was relatively new and I had replaced the hose, so then checked the funnel. Viola… minute cracks and indentations. Replaced the funnel and problem fixed!
Hope this helps! I’ve attached a couple of pics - sorry about the center graphics - they are photos from a video. Cheers