cannot fill water holding tank past 3/4

For me the problem is not so much the fill port being on the side of the tank but that the vent port is on the side of the tank. The vent port really needs to be on top. When you fill the tank the vent port eventually gets covered and then the remaining air in the tank gets pressurized as more water comes in until eventually the air starts forcing the water back out the fill and vent tubes. When I fill mine now, I try and get the trailer set of that the vent side of the tank is higher than the other side. I can get alot more water in this way.

Roam1 what is a cyphon breaker sp?

Make a loop in the overflow hose that goes 6 inches higher than the top of the tank then back down.
Put a cyphin sp? Breaker in the loop at the top
Now you should be able to fill it to the top

Thank's to all for the quick replies,I agree Pappappy 70 gallons is alot more than we need.We mostly boon dock and 50gallons is more than enough,Tried at first towing with half a tank and had to really tighten the sway bar's to control the sway from all that sloshing.Was told I should always tow with a full tank or empty tank for better handling.Still experimenting that one.As for how level the trailer is at fill up may be key too as the fill tube is on the curb side and is about 2 inches lower than the other side.Definitely will try leveling better and measuring the water flow as well.Thank you all

On my Rockwood, the vent hose was too long and sagged lower than the tank and filled with water. This made it hard for air to exit the tank and impeded the fill. You might check the routing of the vent line, but as skipnchar posted, a slow fill rate (allows air to exit through the fill opening) should have circumvented the problem.

Steve

One additional thought, Is the RV fairly level when your filling it? Depending on where the water fill line is attached along with the vent line, it could be that the water is covering one of these after the tank fills to a certain level and causing back pressure when the water is trying to go in. Just a thought.

My water thank also has a side fill connection, so we never actually get it FULL.

Probably about 90%.....up to about an inch from the top. I never noticed any sloshing, but then, I'm about 30' away in the driver's seat:)
It would have been nice if they had the tank fill from the top, but it is what it is.

With the mfgr 250 miles away, you may want to contact them, and ask:
1.) can they do something about this problem?
2.) How long would they expect that repair to take?
3.) Would you be able to stay in the RV during repairs (if you drive there)?

If they answer with numbers and an affermative response for sleeping in the RV, you may want to just take a mini-vacation to have the work done.

Personally, I'd be content with the water you have....most of us have 50-55 gallon tanks, and probably only hold 45-50 gallons....so you're still carrying more than most. And, do you plan to do a lot of boondocking, or are you going to be going to CGs where you can hook up to water most nights anyway?

Happy Camping:)

If slowing down the flow doesn't cure the problem then I'd also have to wonder if the tank isn't actually full. I am assuming it's a gravity fill so the tank should never be pressurized. I suppose if the supply hose is kinked it COULD pressurize enough to force some water out the breather but the cure for that is usually slowing the flow. Might do some testing and determine just how many gallons you're getting in the tank. Measure the time it takes to fill a one gallon jug then time your fill and do the math.
Good luck / Skip

Are you going by the Fresh Water Tank level monitor to get the 3/4 reading or can you visually see the tank is only 3/4 full. The monitors are notoriously inaccurate.

If you have visually confirmed the tank can only be filled to 3/4 it sounds like a manufacturing defect. To get rid of the slosh sound you could wrap the tank area (if you can get to it) in a sound dampening material/insulation like Dynamat