I have the 9 watt which is the same. Mine came with an internal water pump.Yours should have also come with one. If you also have one, submerse it in the tank, then connect it to the intake side of the sterilizer with the proper size hose. Attach another hose to the return side of the sterilizer and direct it into the tank. Intake and return sides of sterilizer are indicated by an arrow showing direction of water flow.