I always fill my canister full of water before priming and I think the intention for the primer was to pull water into the hose not fill the canister.
I've been doing it this way on 2 different 2026s for over a year, without issues.Yes...fill the filter with water...then place the motor (top) back on.
Do this in the kitchen sinkI usually fill it all the way...pop the top back on and water spills out the side as the o-ring is making the seal after I clamp the top down. Then plug it in and its fine.