An apparatus for covering or sealing Storz-type outlets is shown and described. The apparatus includes an outer cap portion having a continuous sidewall, a connector portion for connecting the outer cap portion to the water supply assembly and a sealing cap portion rotatably coupled to the outer cap portion and located at least partially within a void defined by the continuous sidewall, the sealing cap portion including a pliable sealing portion for forming a seal about the water supply outlet. The connector portion includes a pair of lugs and a pair of ramped lug guides associated with an inner surface of the continuous sidewall. The pair of ramped lug guides are provided for receiving a pair of lugs of the water supply assembly. A nut portion extends from an outer face of outer cap portion for engagement by a tool such as a wrench or socket for rotating the outer cap portion about the water supply outlet.