You will need a check valve assembly to hook up your pump to your plumbing out of your Aquascape Designs skimmer filter. The check valve will prevent water from draining out of the Biofalls filter when you remove the pump. It also simplifies pump removal with it's union fittings. Please specify what size pump and aquascape skimmer you will be using the check valve on. Check Valve-2 inch for most Aquascape Pumps Check Valve- 3 inch for 10,000 GPH pump ponddepot@msn.com Copyright - All World Rights Reserved Pond pumps, Pond Kits and Pondless Waterfall kits, Underwater Pond Lights. Aquaclearer Extreme bacteria and String Algae Buster and pond fish food. Pond Depot provides Do-it-yourself pond kits and Pondless waterfall kits delivered right to your home at great prices! Thank you for shopping at Pond Depot you online pond superstore!