vent pipe for fresh water

bpounds wrote:
If we are talking about a gravity fill port, the problem is often with the fill hose itself, not the vent. The fill hose needs a good slope to it, and if there is a low spot, or if it is simply too long, filling will be slow. There may not be much you can do to change the hose. What helps is to slide your garden hose down the fill port. They sell a short piece of vinyl hose for that, and they work well because it is very flexible, or you can just make your own with an old piece of white water hose but that will be stiffer. Either way, the goal is to keep the stream of water flowing fast through the low point.

There can be a problem with the vent hose, but less likely. If it has a low point, it can be blocked with water sitting there. All it needs is to be blown out. But that's rarely the real problem. Air has to come out obviously, but it doesn't take a large hose to pass a lot of air.

^^^^ This!
Mine had a very low location for the gravity fill/vent port & city water connection - it was so close to floor level that it was nearly impossible to get the tank fill hose on/off of the fitting. Both the fill and vent hoses were intertwined around each other, and both had to go up and over the base of the cabinet into the next before going down through the floor. The fresh water tank was immediately below the floor. There was no, NONE, slope and the up and down created low spots in the vent for water to get trapped and block it. Filling the fresh water tank was nearly impossible. I tried straightening out and untangling the hoses with no improvement. The truth is, water MUST run downhill!

I found a much higher location above the existing gravity fill, purchased and installed a new gravity fill/vent fitting about 24" above the factory fitting. I moved the vent and fill hoses up to the new level, rerouting and untwisting them so each had a straight shot down to the point where they went through the floor to the tank. I blocked off the now unused original gravity fill fittings.

Now the water goes in without any problem, and you can feel the air venting from the tank throughout the whole filling process. I still use the filling attachment with the short clear tube and shutoff valve to prevent splashing out at full water flow.

If you have