A liquid distribution system is configured to deliver a disinfectant solution to a medical device within an enclosure. A disinfectant concentration measuring subsystem includes a mixing chamber, a reservoir, a reservoir cap, a pump, and a concentration analysis assembly. The first mixing chamber is in fluid communication with an outlet of the liquid distribution system. The reservoir is configured to contain a reagent solution and is in fluid communication with the mixing chamber. The reservoir cap includes a static member, which is configured to couple with a supply conduit and a return conduit; and a rotating member, which is configured to rotate relative to the static member to couple the reservoir cap with the reservoir. The pump is configured to simultaneously pump the disinfectant solution and the reagent solution into the mixing chamber. The concentration analysis assembly is operable to determine a concentration of disinfectant output from the mixing chamber.