Replacement flick mixer in Jayco camper-trailer

Our 2003 Jayco Penguin has a U/S hand pump for water from the tank, connected using 1/2" clear plastic tubing. It also has a dripping mains tap (connected via John Guest fittings, from what I can see) to the mains pressure inlet on the side of the van. Failure of the hand pump and mains tap seems to be a common problem, and a search of the internet suggests that a common fix is to replace the mains tap with a cheap flickmixer from Bunnings (about $30). The Bunnings Flickmixer comes with two standard "easyhooker" braided lines with 1/2"BSP threaded female connectors to suit household domestic plumbing. Connect the John Guest pipe to one inlet of the Flickmixer, and, after installing a 12v inline pump (with pressure switch) into the hand pump hose using a T-piece, put the outlet of the pump to the other inlet of the Flickmixer. This all sounds great, but none of the internet articles explains what fittings you need to deal with all the changes in pipe and hose size. Has anyone done this and got any ideas please???