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.