In doing a re-plumb for a mobile home that originally used the
blue polybutylene 3/4 water line, I notice that a connection just
outside of the water meter box was made by using a 3/4 compression
coupling as is normally used on 3/4 PVC as a repair coupling.

I assume it was done so that the lenght of blue poly inside
the water meter box could be adjusted by an inch or two
when the water meter was installed 30 years ago. ( The water
meter has been removed )

My question is : Is it normal to use the plastic PVC compression
coupling
to join blue poly, and is it a recommended method....?????

The fitting I saw had been in place for 30 years and there was no
evidence of leakage or any problem. I am replacing the blue poly
with Sched 40 3/4" PVC as an upgrade.

Thanks.