Underwater Warehouse offers a new membrane air diffuser assembly that features a hollow base that can be filled with sand or gravel. This eliminates the need for bricks and straps to get the diffuser to sink! Available in both a single head or dual head assemblies. A 3/4" female threaded outlet is located in the base of each diffuser. A 3/4" x 1/2" poly barbed adapter is included (non-weighted tubing).