delta r10000 connections to pvc

I have an old pier and beam rent house that was replumbed when the bath was remodelled. It has new PVC on the cold side and CPVC on the hot. A Delta R10000 single handle valve body is in the tub which I believe has a brass body and 1/2 inch male threads. Coming off on the cold side is a 1/2 inch threaded PVC fitting which is attached to the supply line, glued 1/2 inch pvc. So far I've had 2 of these fittings leak.

The first time the 1/2 inch pvc fitting was cracked probably from overtightening on the brass threads of the valve body. This time the new pvc fitting looks like it has about 5 small pin holes in the side of it spraying out water.

It's a royal pain to get to since the wall is freshly tiled and I'm coming in from an access hole behind the faucet body. Would I be better off using a 1/2 inch cast iron union on the valve body side and then a male threaded PVC fitting to attach the glued pvc side connection? Thanks.

I don't like unions burried inside of a wall...not sure they're legal, either (somebody more familiar with the codes would).

Female plastic threaded fittings are very prone to splitting and should be avoided.

Don't use CI....

You could use a Sharkbite fitting to connect things. http://www.cashacme.com/prod_sharkbite_pushfit.php HD carries them. Or, one of their other pieces, depending on what you've got.

You've got a few problems...
You're not supposed to have PVC inside the house.
You definitely don't want to bring galv. into the mix. Unions in concealed locations are a no-no!
And it would be nice if you could find a transition adapter like they make for CPVC.

faucet

Unfortunately, you have a system which was installed by someone who wanted to do it the easy way, and did not know the correct way. You do not screw PVC adapters ONTO pipe threads. The fitting will split even if it is not overtightened. I do not think they make PVC sized Sharkbite fitting. And if you are lucky, this is the only place you will have problems with PVC piping inside the house, but do not bet on it.

Fix

so what do you think of going with a 1/2 inch brass union to come off the cold side of the R10000 faucet body? Then using a fitting that is male PVC threaded on one side, which will go into the brass union, and regular 1/2 inch pvc glue joint on the other end to connect to the existing water supply?

I know it's not the best but Like I said this is in a freshly tiled shower and I'm working from a small access hole in the sheet rock on the back side a few feet above the faucet.

A union is not allowed in a concealed location. (I.E. walls & ceilings)

fitting

Tell that to the plumbers who install, or have installed, bath faucets with intergral unions. I do not trust any PVC thread. The female ones crack because of expansion and the male ones crack because of stress. A schedule 80 threaded one end nipple glued into a slip coupling is the safest connection. Use a brass coupling on the valve instead of a union.

coupling

OK what kind of brass coupling? I picked up a brass 1/2 inch threaded union today that I was going to use in place of the galvanized one I had in mind. Remember, I'm going from 1/2 inch threaded male faucet to 1/2 inch glued PVC and yes it's in a very tight spot.

So my plan was to thread the PVC male threads into the brass union. Prime the female side of the PVC fitting. Then thread on the brass female side of the union on the faucet. Next I'll glue the 1/2 inch PVC supply line into the PVC fitting.