We don't change our habits or routines when on FHUs or not.
I only mess with dumping once a week so grey stays closed so it is just as full as black come time to dump.
Some folks leave grey open.....then close day before dumping black so grey tank has some liquid in it.
Some folks even with FHUs use on-board pump and fill fresh water tank as needed.
We use the city water and an WATTS pressure regulator
Funny thing about RVng........pretty much no right or wrong (except for black tank valve---leave it closed).
Figure out what works for you and enjoy the camping.