Check valve units having one or more sound attenuating members are disclosed. A check valve unit includes a housing defining an inlet port, an outlet port, and a chamber in fluid communication therewith thereby defining a flow path from the inlet port through the chamber to the outlet port. The chamber includes first and second valve seats and has a sealing member disposed therein that is moveable from a position seated on the first valve seat to a position seated on the second valve seat. A sound attenuating member is disposed in the flow path downstream of the chamber, within the chamber, or both. In another embodiment, the check valve unit includes a Venturi portion in fluid communication with the chamber. The Venturi portion has a fluid junction with the flow path downstream of the chamber or forms the discharge section of the Venturi portion thereby defining the outlet port.