About to fit a Mira mode digital shower and bath filler. The old plumbing is 22mm going to a Stuart turner pump. I'm removing all the old 3/4 stuff back to the airing cupboard. Gonna fit a Surrey flange which the ST never had, seemed to work ok for 20 years lol. Am I right in thinking all the gravity fed pipe should stay at 22 as far as possible ? Reducing to 15 right before the digital processor.