The UV light needs to be attached to the output side of the pump. That's really all that's important. To attach it you need to get the proper sized PVC fittings , I would suggest that you take the pump and light to Home Depot and let them pick out the parts you need. The pump is 1/2" and depending on the light it could be 3/4" for the 10 watt model which is probably what you have. It doesn't matter which side of the light that you connect to the output side of the pump as long as the water gets through the light. The decision you need to make is how far from the pump do you want the light. Then get some plastic pipe or tubing or even a garden hose and put the proper sized fitting on each end. Connect one end to the pump and one end to the light. Next where do you want the water pumped to? Once you decide that put a piece of tubing or hose on the other end of the UV light and direct it to where you want the water to go.