Some basics that apply to all filters which have the impeller/pump at the top of the canister, should work on all.
Think of what it takes to make a siphon work and then apply it to the tube taking water from the tank to the canister. Water runs downhill, right? so manage to fill this intake line with water, but leave the rest of the system empty.
The manuals I look at here:
Indicate two methods that they recommend. Page three/diagram "H" indicates using a sucker to drawn water through the system, while diagram "H1" indicates you can fill the intake tubing through the top if you have the intake with opening at the top.
But the idea is that water will run down this intake, fill the canister from the bottom to the top as it forces air up and out the outflow. This will only happen if you leave the canister empty so that the air can move past and not be blocked by water in the can or outflow tube.
Siphons are simple and we should all be able to do that or get into another game!
But where we tend to mess up the program is when we leave water at some point along the line so that it blocks the air from moving out. Engineering students will certainly argue that air is less dense than water and all kinds of high level techie talk but it doesn't take much to find that is WILL NOT go down through water to come up!
Where we often run into trouble is the way we place things like reactors which hold water, inline with the output tube. Leave that water in the path the air needs to use to go out and you are quite likely to have trouble priming.
Keep it simple. Water runs downhill and air will go up if the path is open.
To fully clear the small amount left after priming, some like to tilt the can to let that bit get out, but leaving it alone will let it work out after a short time, but ONLY if you have done it right up to that point.