An apparatus is presented that includes a body and a membrane. The body defines an externally hemispherical body portion with an orifice, as well as a channel passing through the body and terminating in the orifice. The membrane is formed at least in part of an elastomeric material and overlies a portion of the externally hemispherical body portion. The membrane defines a plurality of holes therein, and a plug that is inserted into the orifice and the channel. When submerged at the bottom of a wastewater treatment tank and in gaseous communication with a distribution conduit providing compressed gas, the apparatus may function to release bubbles into the wastewater. When the compressed gas is turned off, the apparatus acts as a check valve that stops water from entering the diffuser and the distribution conduit.