Improper intake design:
The fill line is too long, too short, or too small in diameter, resulting in insufficient slope between the fill and the tank.
It is necessary to vent the tank as air enters the tank to make room for the water. There is a limitation to how much water can be released from the tank at one time due to the vent lines being narrower than the fill lines. The RV owner has the option of spilling water or turning the faucet down to a volume the RV tank can handle if the amount of water trying to enter the tank exceeds the amount of air trying to escape.
FIXING A SLOW FILLING RV FRESH WATER TANK
CHECK FOR KINKS
Your RV’s fill assembly, usually on the side, includes a vent hose that connects the water tank to the exterior vent. Make sure it is free of kinks or obstructions. Unscreened vents can get plugged with insects if they are not screened.
You should check the fill hose for kinks between the tank and the fill opening.
Ensure that the fill hose slopes evenly and properly between the fill opening and the tank. If possible, improve your work.
The venting system should be made larger.
Ensure that the tank is filled under pressure by assembling a system.
FILL WATER TANKS WITH WATER FILLERS
You should always keep a supply of water in your RV’s portable water tank in case you need a bathroom break on the way to the RV park, a spare water supply in case you need to fill your radiator in an emergency, or if you are planning on dry camping for one night only.