I have a one inch water main in a residential home, going into a 5/8 water meter, then back out to one inch pex pipe. Right after that, if I were to install a 1/2" boiler drain (aka. sediment tap) off of the pex pipe, and I was to attach a Toro flow gauge, how accurate with the gpm reading be? Would the reading be an excellent figure to base my zones on as far as flow (gpm's) is concerned? How many gpm's could I expect it to be? I have attached a pressure gauge at the hose bib at the back of the home and it reads 55 psi. I suspect that the Toro flow gauge would not accurately measure the gpm's since I am connecting to a 1/2" boiler drain, not directly to the one inch pipe. The hole inside it the boiler drain is pretty small and very restrictive of volume. What do you think?