I've finished my PEX supply-side plumbing rough in.
I put a Schrader valve into a push-connect fitting and attached it to one open end and threaded a pressure gauge into another push-connect fitting and attached it to another open end. Then I connected a hot/cold pair of lines to make a closed system, then plugged the rest of the openings with test plugs and put test plugs into all the shower/tub outlets.
I pressurized the system to about 80PSI. Within a few minutes it had dropped to 74PSI, then by the time I was done with dinner it was down to about 50PSI.
I've listened & felt every single joint in the new plumbing - I cannot hear or feel any air escaping. I've sprayed soapy water on all the joints and I don't see any bubbles forming. I've even tested the connections at the valve & pressure gauge to make sure they weren't the source of the leak.
What other methods are there for finding where the plumbing is leaking?