What is the right of the T for?

So here is basic plumbing diagram.

well--->pressure tank---> supply line

The attached picture shows the link coming off the pressure tank. I do not understand why there is a T junction. The pipe to the right goes extends for approximately 6 inches and is capped. It all appears to be 3/4" CPVC, but again I was not aware you could use a compression sleeve to attach to the copper T. I am not sure how long this has been installed for sure, but I know this setup passed my home inspection when I purchased the house almost 4 years ago.

Since the leak has started it appears from the joints of the T my plan is to replace with all CPVC components. The part that I can not decide is whether to just put a 90 elbow on it or replace with a T. Thoughts on the whole setup appreciated.

That is PEX tubing not CPVC... It wouldn't say Zurn on it by any chance would it?

Pex really? Did not see anything identifying it as Zurn. If it is Pex how have unions from CPVC to Pex been holding up?

pex

The connections between CPVC and PEX would depend on how it was done as far as reliability. There is no item made especially to connect the two. You can use male and female adapters or Sharkbite couplings to do it.

PEX is generally superior to CPVC. I have no idea why there's a tee if one branch doesn't go anywhere unless the installer didn't have a 90 on the truck.