On Fri, 19 Aug 2011 12:52:34 -0500, Pete C. wrote:

After reading several more posts is seems to be that this is a gravity
tank presumably on a hill, with a booster pump near the house.

My fault for not being clear.

The 'only' gravity part of the system is the four inch pipe that goes from
the tanks to the fire hydrant, about 20 vertical feet or so down the hill
(about 150 feet away from the tanks and on the other side of the house).

The rest of the system is certainly pressurized since that four inch outlet
pipe almost immediately (within a few feet) branches off with what looks
like a two inch pipe that goes to a pressure pump and blue tank that is
almost right next to the large unpressurized holding tanks.

So, for all intents and purposes, all the house water, from the pressurizer
next to the holding tanks to the house is pressurized.