Membrane air diffuser assembly that features a hollow base that can be filled with sand or gravel. Eliminates the need for bricks and straps to get the diffuser to sink. Available in single, dual or quad head assemblies. Redesigned base allows for strain relief clamp to secure tubing onto base. Built in check valve prevents backflow of water up air line. Inlet air fitting (included) accepts 3 /8" or 1 /2" tubing.