Folks, if you've recently upgraded or renewed your annual club membership but it's still not active, please reach out to the BOD or a moderator. The PayPal system has a slight bug which it doesn't allow it to activate the account on it's own.
If you do have a bubble, you can keep your hand over the overflow and close off the vent to the drain, let the tank fill up and let it start a full syphon, this will flush it out for sure if thats the problem
do you have a sump still? If so you can mount this above your current sump and just let it drain back into your sump. Feed it with a tank overflow or a powerhead in the sump. Without seeing your setup its hard to say. Prob couldnt fit it under a cabinet this way