Hi,
I've been having a lot of problems getting my new sillcock to thread
into the corresponding copper fitting (Sweated onto the supply pipe).
I have had to re-do the supply several times because the chrome
sillcock (1/2 mip) wants to eat the copper threads instead of going in
peacefully.

Here is my idea for repair and rationale:

12" Sillcock 1/2 MIP, screwed to 1/2 FIP copper fitting, sweated to
short copper pipe, sweated to male side of brass union
Female side of brass union sweated to copper pipe sweated to supply
tee

The sillcock is then joined to the supply at the union instead of at
the copper fitting.

Rationale:
- The male brass union will not eat the threads of the female brass
union.
- The brass union will not seize. Copper and chrome may seize, and in
this design that is actually a benefit. The next guy can just turn
the sillcock out, and with it comes the male half of the union (the
part that is harder to damage).
- The "Wiggle" from using the sillcock will be on the male side of the
union, which is held rigid by the threads, so it shouldn't be possible
to break the union seal by using the sillcock roughly.

Problems:
- The sillcock is screwed in and the downspout must be vertically
aligned for the freezey-proof to work. Conceivably, I can see a
scenario where when on one turn when the downspout is aligned, the
union has not yet sealed, but then the union becomes tightened before
the sillcock is vertically aligned on the next turn.
- Is a union going to be reusable in this situation? If the next
guy's going to have to dig into the wall in any case, I'll just sweat
the whole thing and be done with it.


Another idea was to sweat a 1/2 male fitting onto the supply pipe, and
then attach a threaded copper coupler to the sillcock and use the
copper coupler to connect to the male supply fitting. Copper on
copper, so no seize and no eaten threads, but I don't even know if a
threaded copper coupler exists, much less if it would be possible to
seal the threads.

Ideas? Flames?