cpvc pipe not standard size?

I'm having some difficulty connecting some new cpvc pipe to some existing pipe. The existing pipe might be pvc, might be cpvc, I'm not entirely sure, and I'm not really sure how to tell, or what the difference is anyway. The existing pipe is close to 3/4", but just a couple hairs smaller, and it doesn't seem to be able to make a watertight seal with the new pipe. Any ideas about what I can do with this? If it helps, this is for washer h&c supply lines. Thanks a lot.

PVC and CPVC are not the same size at all. PVC is not legally used anywhere inside a structure for water supply piping. Also, the solvent cements are different, so you could not join the two with glue-up fittings. Mechanical joints must be used, like compression or a union.

Just to clarify, how are you trying to join the new pipe to the old? With a coupling? Also, are you talking about the outside diameter of the pipe or the inside diameter of the pipe? It would help if you could give accurate measurements for pipes you're trying to join.

FWIW, the outside diameter of CPVC is less typically less than the equivalent sized PVC, which is iron pipe size. I say typically because there is an iron pipe size CPVC.

There is an all purpose cement that's supposed to work on cpvc or pvc however cpvc & pvc aren't the same outside diameter . PVC is usually white & CPVC is usually cream color .

Sorry for the confusion. I'm new to all of this, and after trying to figure this all out, I realized that the existing supply pipes are 1/2" PVC pipe. Should I open up the walls and replace this with CPVC, or should I just stick with PVC?

If it's pvc replace it . pvc isn't supposed to be used inside the home & pvc isn't supposed to be used for hot water .