How come you guys are filling your FW tank so full? My method for filling is to only have about 15-20 gallons in the tank. I know my garden hose runs about 8 gallons a minute, so I turn it on and let it run into the FW tank for 2 to 2-1/2 minutes. My 8 gpm is because of the 5/8" size garden hose and the pressure we have. Our tank holds 35 gallons.
I took a 5 gallon bucket and timed about how many seconds it took to fill the bucket. Of course we don't use the shower and we have a gallon of clean drinking water in the fridge. We use campground showers or the friends house shower we are visiting.