Outdoor Water Solutions ARS0172 9-Inch Rubber Membrane Diffuser with Base Unit comes with a backflow valve and 1/2" fittings to plug into your 1/2" airline Rated for up to 5 cfm and perfect for lakes or ponds, especially where you're only running one diffuser Base can be filled with sand or gravel so it sinks to the bottom of your pond ARS0172 Unit comes with a backflow valve and 1/2" fittings to plug into your 1/2" airline Rated for up to 5 cfm and perfect for lakes or ponds, especially where you're only running one diffuser Base can be filled with sand or gravel so it sinks to the bottom of your pond