Flushing Duration Calculator This calculation was designed to provide useful information concerning a typical installation. Features such as distribution system design, line materials, quality, and c factor are likely to impact final flushing durations. Line size in inches: Line length in feet: Pressure at Hydro-Guard in PSI: Must range from 10 to 150 psi Days between water turnover one time from flushing: 3 days (72 hours) turnover recommended Flushing Duration: minutes per day