Buy a flowmeter from McMaster-Carr Supply. They have a wide selection of them and they carry a 3/4" NPT model with an LCD readout. You can buy a couple of 3/4" NPT to garden hose male and female adapters from them also.
2006 23B Hybrid with 10k round bar WDH
2011 F150 4x4 SCREW Ecoboost, Max Tow, Integrated TBC, 3.73 LS axle, Firestone Ride Rite airbags.