If you’ve kept fish for any length of time and you’ve used canister filters, chances are that you’ve had a priming issue at one time or another that results from the intake hose not staying full of water. If you haven’t yet, you will. I think it’s inevitable.
Most canister’s sold today have quick release valves that allow you to disconnect the intake and outtake hoses from the canister without having to disassemble anything or worrying about clamping hoses. Furthermore, when disconnecting these quick releases from the canister, water is typically retained in the intake hose, at least to the point where the hose crosses the top of the tank. (Note: This is assuming you’re using a canister the typical way and not connected via a pre-drilled hole in the tank like in an overflow box). While there are plenty of solutions out there for this scenario, here’s one that should work with any canister filter.
If you have a powerhead or small submersible pump, use it to “push” water up the intake tube that is inside the tank. Most likely you have a strainer (see left photo above) or a prefilter sponge of some kind on the end of your canister intake tube inside the tank. Remove it, plug the canister in, then insert the intake nozzle of the powerhead/submersible pump into the intake tube (see right photo above). Make sure the water level in the tank is above the intake tube before you begin. It will only take a few seconds for the canister filter to begin pulling water from the intake tube and evacuate any air.
This solution can also work with a wet/dry, sump type of filter. However, trying it will require some additional steps, which is a post for anther day.
NOTE: Do NOT use a large/powerful powerhead or submersible pump for this. For most canister filters, a powerhead or submersible pump rated at ~160 gph should be more than sufficient. If the pump head pressure is too high, you could blow the hose off of a fitting. That’s unlikely to happen, but anything is possible when you create great water pressure inside a closed loop. All you need is enough pump head pressure to “push” water up the intake until it reaches the top of the tank where the canister takes over and begins the water flow.