A medical device processor comprising: (a) an enclosure for holding a medical device (200/); (b) a liquid distribution system configured to deliver a disinfectant solution to a medical device within the enclosure, the liquid distribution system comprising a liquid outlet; and (c) a disinfectant concentration measuring subsystem comprising: (i) a first mixing chamber in fluid communication with the liquid outlet, (ii) a reservoir configured to contain a reagent solution, wherein the reservoir is in fluid communication with the first mixing chamber, (iii) a reservoir cap configured to couple with the reservoir, wherein the reservoir cap comprises: a static member configured to couple with a supply conduit and a return conduit, and a rotating member configured to rotate relative to the static member to couple the reservoir cap with the reservoir, (iv) a pumping arrangement (406, 408) that is configured to simultaneously pump the disinfectant solution and the reagent solution into the first mixing chamber, and (v) a concentration analysis assembly that is operable to determine a concentration of disinfectant in a sample solution that is output from the first mixing chamber. (a) an enclosure for holding a medical device (200/); (b) a liquid distribution system configured to deliver a disinfectant solution to a medical device within the enclosure, the liquid distribution system comprising a liquid outlet; and (c) a disinfectant concentration measuring subsystem comprising: (i) a first mixing chamber in fluid communication with the liquid outlet, (ii) a reservoir configured to contain a reagent solution, wherein the reservoir is in fluid communication with the first mixing chamber, (iii) a reservoir cap configured to couple with the reservoir, wherein the reservoir cap comprises: a static member configured to couple with a supply conduit and a return conduit, and a rotating member configured to rotate relative to the static member to couple the reservoir cap with the reservoir, (iv) a pumping arrangement (406, 408) that is configured to simultaneously pump the disinfectant solution and the reagent solution into the first mixing chamber, and (v) a concentration analysis assembly that is operable to determine a concentration of disinfectant in a sample solution that is output from the first mixing chamber. (i) a first mixing chamber in fluid communication with the liquid outlet, (ii) a reservoir configured to contain a reagent solution, wherein the reservoir is in fluid communication with the first mixing chamber, (iii) a reservoir cap configured to couple with the reservoir, wherein the reservoir cap comprises: a static member configured to couple with a supply conduit and a return conduit, and a rotating member configured to rotate relative to the static member to couple the reservoir cap with the reservoir, a static member configured to couple with a supply conduit and a return conduit, and a rotating member configured to rotate relative to the static member to couple the reservoir cap with the reservoir, (iv) a pumping arrangement (406, 408) that is configured to simultaneously pump the disinfectant solution and the reagent solution into the first mixing chamber, and (v) a concentration analysis assembly that is operable to determine a concentration of disinfectant in a sample solution that is output from the first mixing chamber.