First, Use a clear hose..

When inserting the hose into the tank try to put more then 2/3 or more of the hose into the tank (probably only works with full gas-tanks)when the hose is as far in the tank as possible put your thumb in the hose to seal it of, then pull the hose out of the tank until you can see gas in the hose outside of the tank, try to get it out as far as possible, then keep holding the shut part lower then the tank opening, hold it before the container and pull your thumb out. If you are doing it correct, the gas flow will pull itself through the hose and will start flowing in your container..

Try it. This is how i clean my aquarium at home...


It's important to put in your thumb AFTER you have put in the hose, because else you can't get that vacuum working..