El Cheapo Gauge-o
You can just put a "T" off your water outlet, and attach some clear plastic hose and run it out of the locker so that it is visible. Cap the tube, but put a small pinhole in to allow air to move, but not so quickly that the tube will leak on heel, or aspirate into the system while the pump is operating (this will tend to happen more if the site-level is between the pump and the tank). The level of water in the hose will match the level in the tank assuming no heel. You can make marks on the hose after adding known volumes of water to the tank if you want more accuracy than "1/2" "3/4" etc. Regards, -Keith
