When you install a mixer in a sink your supposed to put a mini stop cock under the sink before you connect it, if the water should want to flow backwards in the pipe it will actually push the washer back down onto the seat and close it off, simple yet effective backflow prevention with standard fittings. because the mixer is in the wall this is not possible as you cant put a tap into an inaccesable location. The mixer i have in my van is a HANSA POLO flick type for shower and bath, it has non return valves built into the connecting nipples.

LOXEAL is good stuff but i dont use it on tap connections or anything i want to get undone in the future, eg hot water service.... It is a huge pain to undo, also it takes 45 minutes to dry, and has a workable consistency for about 1-2 minutes, screw everything together in this time or let it dry before putting next peice of hardware in, if you move it before its dry it leaks and is still apain to undo.