We have a Groco strainer (medium size) which serves a very robust (compared with a Shurflo) saltwater wash down and the forward head. While our head a is a PHII, there isn't a problem with the two of them served by the same line.

The key, I think, from a hydraulics standpoint is place an intermediary volume which functions like a "sea chest".

Anyway, you should have a strainer anyway.

Beyond that, if the check valve works -- great.