I bought two of the Fluval 305 canisters about 3 years ago. One has never been a problem but the second is a bear to prime and I dread filter cleaning time with that filter. I can never get it going after cleaning it.

Which was today. I tried priming slow and priming fast. I tipped the canister to force out air. I tried filling the canister first all the way full and then half way full. I must have taken it apart 5 times, cleaning the impeller, making sure strainer didn't have crude in it and finally tore the hoses off the tank and cleaned them out in my bathtub. (About 100 dead cherry shrimp fell out.)

Get the bloody filter back together and nothing! So I went in search and some guy wrote a post 3 years ago saying to suck on the output hose a couple times. I'm like, "oh yuck". Well, I did it. Two little pulls on that output line and the filter took right off. I didn't suck water or crap out of the line.....but apparently I sucked out an air bubble! (I has quite happy I cleaned the lines today.)

Fortunately, this only happens a few times a year but I sure will remember his advice in the future. Fluvals are dead quiet and filter well but these air locks appear to be a common problem with some of them.