Double check valve location?

[Super_Paulie]

gentlemen.
im looking to feed a external taps for the garden etc, with the feeds coming from my domestic manifolds. But it poses a few questions... Id need to chase the block to get the pipework up to where it exits the house, so id be using a copper wallplate/tube with the half inch thread for the tap. 
 

It would mean i would lose my "one, continuous feed" from manifold to outlet in my plastic layflat as obviously it will need to transition from plastic to copper under the floor, which is indeed a shame. But additionally where would i put the double check valve? The taps i want to use are Peglar levers so have no built in valve, should i just add that at the manifold end as it would end up under the floor or chased in which surely isnt the best way to do it. As the pipes will be exiting essentially in the middle of the lounge its not like it can all be concealed in a kitchen unit so it will have to be chased. Either that or come out at under-floor level and then up the wall externally which im not keen on.

Any genius thoughts welcome, i cant really think of any other way to go abouts this but just thought id throw the question out there. Image attached

[Conor]

Take your tap feeds off between the main stopcock and your cold water manifold. Otherwise you'll be disappointed in the flow rates if coming via a 15mm manifold and pipe.

 

Tee off your incoming 20/25mm pipe and run 25/20mm MDPE underground to each to location. 

 

You can get taps with integrated double check valves.

[Super_Paulie]

Thanks Connor but I've had my feeds on 15mm the last decade and I'm happy with it, it's enough for washing the dog. It's also 2 feeds, hot and cold.

 

I already have my taps, it's more the transition from full length plastic to copper, chasing and check valve location I was hoping for opinions on.

Cheers though 👌