erm.. for mine there is a pump on the canister that can pump air out. i dont knoe how yours work. there will be a gushing sound when the pump is starting to get filled it water, after that all the bubbles will come out and the canister will be quiet.
haha are u using a spray bar ? if u are then its abit weird leh. normally if the canister is ###### in air.. the bubbles will come out from all the holes of the spray bar, yours come out in a stream lolz.. sorry sis in this case i am not too sure wat the problem is. u might wanna check the pipe which water is being suck into the canister. see whether its tight and no air are getting in