A client has fitted his floor boards but hasn't had any plumbing done and he doesn't want to use pushfit

You weaken the joists if you to that... because that is the most critical point because they are under tension (The top half is under compression)... cut them deep enough anyplace and the floor can collapse under load.

Hang them below the joists... even if it means lowering the ceiling.

he doesn't want to use pushfit..

What does that mean?

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Harold is correct, can't notch top or bottom but can bore in the core area as described in Harolds attachment. I'd use PEX which can be crimped

What does that mean?

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I assume Gator or Shark bite.