I have to join 1/2 inch copper to 1/2 inch cpvc and the
'clerk/salesperson' at Home Depot sold me on using the Push N Turn
couplings. Well I've now used up 3 of them (they're non reusable
items)and I still have a leak on the cpvc side!

I don't know what a Push and Turn coupling is, but as the other posters
have said, the best solution is to use the appropriate male/female
adapters.

DO NOT use the CPVC "female" adapters that have the threads cut into the
plastic. I don't think they are allowed by code anyway. I've tried them in
the past and when the metal "male" adapter is threaded into the CPVC
"female" adapter, it cracks the female adapter. Happens almost every time,
no matter how careful you try to be.

You could use a MALE CPVC adapter threaded into a copper FEMALE adapter.
I've done this a few times and have made many connections that work fine.
However, the expansion rates of the two materials is apparently quite
different and over time the connection can start leaking. I haven't
experienced that personally, but I can see how it might happen.

The best solution is to use a "CPVC Transition Union" specially made for
the connection. They have a brass fitting on one end, a CPVC fitting on the
other, a neoprene gasket in-between, and a threaded piece that holds the
two halves together. These come in several configurations, with male or
female fittings on the metal end, or even brass drop-ear elbows. I've used
a LOT of these fittings. They're easy to install, and I haven't had a
single leak from any of them.

Here are couple of examples of the transition unions: (watch the word wrap)

http://www.cornerhardware.com/item_2.../2-Transition-
Union/item.html

http://doitbest.com/shop/product.asp...660L8VNFSRSD6F
09&dept%5Fid=1592&sku=465275

These fittings are usually located with the CPVC fittings in the home
centers. The only real negative is the price. They cost a few dollars each.
But, they're worth it.

Anthony