reziztor said:
I read on the internet to start sucking on the return hose... Been doing that for 30 minutes with nothing!
Check to see all valves are open.
It is actually easiest to start with the canister with no water in it, and with all hoses empty as well. Be sure that the input and output lines are connected correctly, input goes in the bottom of the unit, output is off the top of the canister. Be sure all hoses are on correctly.
It is easiest to start with the output spray bar above the level of the water in the fish tank, as air needs to escape there and though it can if the spray bar is under water, it can make a mess. (If the output is very far under water it may not be possible for the air to escape, so if the spray bar is on the gravel, you will have problems and may need to do another way.)
Be sure all valves are open, then connect the input to the canister. Have the output line ready. Suck on the exit from the canister, at the valve connection, one pull and you should hear water starting to fill the canister. You have a few minutes to get that output line connected correctly -- have a towel ready in case you have trouble!
Be certain before you start that there are no loops in the hoses, places where a bubble can be trapped, you probably need to trim the hoses to give you just enough to pull the canister out from below the tank, no more. Any bubble in the input line will stop the siphon losing the prime.