Only fill the intake btw, by filling both you run the chance of creating a vapor lock.
Also, Make sure there's no loops, kinks or any slack in the tubing (cut it to fit, this also improves flow rate.)
Make sure the the tank is full and all the fittings are pushed together firmly (air breaks syphons.)
On the output, make sure there are no U's or places for air to get stuck. It should loop over the top and do a 90 degree turn to make the spraybar horizontal at the most.
Unplug it, drain it, and slide the connector back into the canister (keeping the handle up to block the flow of water,) unscrew the intake cap, add water untill it's full (it will ususaly take only one 21oz cup of tank water,) quickly screw the cap on, push the connector firmly into the canister and lower the level, water should (maybe slowly at first) start pooring into the canister and bubbles should exit the return line into the tank. After 2-5 mins, turn the canister on, walla.
Also, it wont work right unless it's some number of inches (I think around 24) below the tank.
You'll never need to remove that cap and add water to the intake again unless it sucks alot of air into it somehow, cleaning it is a breeze.