I got to fit a outside tap to the back of my house .The pipe will have to  run on the outside wall to the tap.Is it best to run in copper or polyplumb pipe.

nyck

DCV = dual check valve

You'll also need an isolating valve inside the house for winter (or whenever) isolation.  That's when you drain it off too.

Nothing more to add, use copper and clip every 1000mm. fit drain cock at the lowest point and insulate well. Jobs a good un.


btk

Double check valves stop water flowing in the wrong direction in the pipe. These are one of the main reasons you can drink from the tap in the UK. Imagine you have a garden hose on a tap, sitting in a puddle of water, which is there because the drain is blocked after the rain. Further down the line theres a guy using his pressure washer for half an hour, thing is you dont have very good mains pressure where you live, so the pressure washer "sucks" the mains through, as you are on the same run it sucks your supply back towards his own. Just then you go to turn on the outside tap, hmmm no water, meanwhile just opening the tap has meant the guy down the street can suck all the water from your hose into the building, all the drain water is now flowing thru the (potable) water pipes in your house. The guy just stopped using his pressure washer now, jast as the last drop from the hose gets into your drinking water. fancy a coffee?? lol
Double check valves stop all that happening! lol

You have the right idea for running your taps, try to keep as much pipework as you can inside the building though. Nothing wrong with feeding both taps from one valve&check valve.


btk