View Full Version : Fresh Water Tank Capacity

Uncle Rog
01-10-2007, 10:36 AM
Howdy, I have tested and re-tested and my tank will only fill to 45 gals, period. I am talking with the factory and they do not have any idea what is up at this point. Has anybody else accurately measured the capacity? I know timk has, but somebody else must have also. My tank was broken on delivery and repaired maybe that is a problem? help.....

2 Cats
01-10-2007, 10:00 PM
Hi Rog,
I'm not sure if your tank is like mine, So this may be of no use.On my Cyclone there are 3 vent lines 2 at the rear & 1 up front. I put shut offs on all 3. When I fill the tank I have them all open as water runs out of them I close the valves 1 at a time till water runs out at each. I also checked my capacity in a 7 gallon can. Before & after installing the valves first try was right around 70 gallons 2nd time was right around 107 gallons which is close to where it should be. The valves I used are 1/4 turn chrome lav.valves with a 3/8 hose barb on one end around $4.99 @ home depot. Remember when you get where your going to open the last valve you closed if it runs longer then a few seconds close it till you use up more water then open it again. depending on what were doing I've waited 2or3 days boondocking before I could leave the valve open. If you need more info. let me know I'll try to help.
2 Cats

01-10-2007, 11:59 PM
So where do these vent lines hide? Are the up in the underbelly area hidden by the covering?

All I see from under my 5th wheel is one with a 1/4 turn which I am pretty sure is the fresh water drain and two that have caps on them which I am pretty sure is the low water drains.



B. Lee
01-11-2007, 12:17 AM
I have thre vent lines that protruede through the under belly. I am wondering if each corner of the tank has a vent line. If so I have one line that is still above the underbelly.

01-11-2007, 06:53 AM
My unit has three vent tubes that hang below the undercovering in the rear behind the left side wheel. The fourth vent line (yesa I believe there is a vent at each corner of the tank) runs up to the tank fill opening in the docking station. I connected these three in the rear to a single shutoff valve that I close after filling the fresh water tank to transport the trailer.

I then have two tubes below the undercover near the docking station. One has a brass shutoff valve that is a drain, and the other is open, and is the one that can be used to drain the fresh water tank using the water pump and valves in the docking station.

I don't recall the exact valve orientation to use the pump to drain the tanks, but have it somewhere in my paperwork if you need it. It might be in your trailer manual, and I think someone may have posted it in PDF on this forum.

Uncle Rog
01-11-2007, 10:59 AM
Howdy Guys, thanks for the replies. I have two vent lines behind the road side duals, Chris at HL says they are tied into the other vent lines? I do not know if the fix they used to repair my tank is involved or something more complicated. I am working on getting it in to be fixed, I guess I am a little old fashioned, but I think it would be nice to fill the tank to full capacity and go camping without having to add valves, lose water or worry acout blowing out a tank by guessing every time I fill it. My literature, and partial motivation for my purchase,says it has a 75 gal tank, now I am told it is 63 gal with a 12 gal water heater? However timk in his detailed testing has a 73+- gal tank with the added valves etc.....I will get this sorted out a give a full report when completed.....UR

01-13-2007, 02:41 PM
We are in AZ boon docking at a camp ground. I brought along 4 five gallon water jugs and a pump to haul in good water. I had the tank braced before I left and have the vent valves with shut offs. I put in 20 GALLONS just to start the day. Couldn't get the pump to prime! went and got 20 more gallons and then the pump started to work. It took 12 gallons to fill the water heater and soon after using water the pump quit working. Went and got 20 more gallons and things started to work again. I surmised that it takes at least 20 gallons to reach the pump intake. A BIG waste of water as far as Im concerned! I did fill up the tank until the first vent started to flow. Figured I could get in at least another 10-20 gallons before the others would flow. I figure I put in close to 80 gallons in the fresh tank, but 20 of those are not retrievable.
p.s. The fiver is LEVEL!

01-13-2007, 05:46 PM
Our tank holds 66 gallons when the vents start to flow.
When I shut down the 3 lower vents the tanks holds 75 gallons.

01-15-2007, 12:56 PM
Those tanks are so long and shallow that if you aren't in a perfect situation the water is going to be on one end or the other when there is only a few gallons in it and I am guessing the pump intake will not retrieve them. Not that I think 20 is a few gallons! Next spring the bottom will come off again and I am going to see if I can redo the pump intake to pick up better when it is lower than 20 gallons. I have rigged up a neat way to fill the tank when boon docking so its not a real big problem right now.

Uncle Rog
01-15-2007, 01:01 PM
Hey Chopper, hope you are enjoying the AZ. That would make sense if the pump intake does not pull from the bottom of the tank no one could use all the capacity of the tank !!!!

01-15-2007, 03:28 PM
I'm going to ask a dumb question but how about hooking the pump intake to the drain? That might be a way to get all of the water out of the tank. Put a "T" in the drain line with two valves and you could use it either as a drain or as the pump intake. Just a thought.

Uncle Rog
01-15-2007, 04:05 PM
Great idea JP, but I am still under waranty and want it fixed right....

01-15-2007, 04:08 PM
I'm going to go out on a limb here, but I think the drain and pump hookup, are at the same height on the sides of the tank.

01-15-2007, 04:15 PM
Hi Tim;

Could very well be. I haven't pulled the bottom off of mine to check. On past fifth wheels, my drain came out of the bottom of the tank.


01-15-2007, 08:28 PM
My rig is now back at the dealer for warranty work. One of the issues is that I can never get the pump to pick up water from the tank. I have not boon docked so all I have done is put water in the tank for "on the road" use or for freezing nights that I want to disconnect the hose. I do not fill the tank for this, just attempt to fill it to about a 1/4 tank. It just does not make sense that the pump will not prime unless the tank is close to full. From the other post on this forum, I guess I am not the only one with this problem.

01-15-2007, 09:18 PM
I also wonder if the pump and drain arn't connected in some way as when the knobs are set for drain in the docking statioin, mine seems to pump out the drain tube..../Doug

01-17-2007, 12:10 PM
I've been at a campsite for 10 days in KY and the water is shut off at the sites. I have been filling four 5 gallon water cans at the camp office, driving back to the site and filling the water tank. I hooked up a funnel and hose, but have to lift the 5 gallon jugs up high to pour.

Has anyone else come up with a good idea on how to do this?



01-17-2007, 02:31 PM
Home Depot, Lowes, seasonally at Walmart, etc., has small 110V pumps for water gardens and fountains. Look for one that you can attach a 3/8" or 1/2" clear vinyl hose to for pickup and discharge. The smaller pumps will have the smaller nipples. Used them for years and they work great, one lasted about 12-14 years, about $25 at the time. Now they're in the $30-$40 range. If you have an option for a self priming pump it is better and easier.

01-17-2007, 03:35 PM
Jon,I use one of these http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=9576 from harbor freight and made the wires longer and hook it up to my truck batter and fill the tanks. Only $40 and it will empty a 5 gallon jug in less than 2 min.

01-17-2007, 04:10 PM

If you end up getting a pump, some sort of water bladder, like this (http://www.campingworld.com/search/index.cfm?affiliateID=577&siteID=CRmXdm5X5mI-ytOI6qSyt.ZckqnQZ.zhQA&action=search&keywords=1605) will save trips if you have room in the bed of the truck.


I like that pump - thanks for the link. If one was to use a water container (bladder) in/at/on the car/truck and pump through 25 feet of hose, would it be best to put the pump nearer the source and push it to the tank or nearer to the water inlet on the trailer and pull it? I am guessing at the truck so the head-pressure in the container can assist a bit. No experience doing it though.

I have 12 VDC available in the UDC on the trailer and can easily get 12 VDC at the truck bed using an adapter on my 7-wire receptacle.


What about filtering water drawn into a portable container for refilling the RV tank? I have a 2 stage filter I use for pressurized shore water connections. I'd prefer to clean the water up that comes from the communal supply before I use it. If there was ample pressure at the communal supply (there has been at one place I do this at), I'd filter it then. Where there is not ample pressure at the supply to push through a 2 stage filter, I am wondering if a portable pump has the capacity to push water through a filter as I draw it from my portable container/bladder?

Thanks all - great thread.


01-17-2007, 04:37 PM
Jim, i don't know the answer to your question, but i would say that if the question can be answered, it will be answered on this site. This is an amazing site.

Uncle Rog
01-17-2007, 05:23 PM
We use a charcoal filter canister type filter when filling the tanks or using city water, am considering a 12v pump for refills because of my problem of not having a 75 gal water tank, in concert with a 15 gal drum.......

01-17-2007, 08:28 PM
Thanks everyone...my back feels better already looking at the pumps. This site is so helpful.

I am breaking camp in the morning and headed back to New England and the snow.


01-17-2007, 08:28 PM
You already have everything you need. Pop off the panel behind the docking box. Then just turn a couple of valves to cause the pump to draw from the winterizing tube, rather than the tank.
You can use the water directly from the jugs, or just pump it out of your jugs into the water tank with your garden hose, by sticking it into the hose fill. You'll be surprised how quick it will empty a jug.

01-19-2007, 10:08 AM
Excellent idea....I will try it this weekend!


Uncle Rog
01-19-2007, 11:58 AM
TIMK, I wonder if the water pump is tough enough to run for that long with out wearing out premateurly? I have never wore one out before, I just wonder?

01-19-2007, 01:01 PM
I suppose there would be more wear on the pump, pumping your water in and out. There might be a expected lifetime rating somewhere, if a person knew where to look. I don't recall ever wearing one out.

I was just pointing out, that you don't need to get anything new, or haul anything extra, to get the job done. If your pumping 50 gallons in and out every few days or so, I would think a seperate pump would be a good idea.

Uncle Rog
01-19-2007, 04:08 PM
Point well taken, I might try it out this weekend in the driveway, might even be cool to add some hose / valve to where you could switch with out pulling the bulkhead.......

01-19-2007, 06:32 PM
Moving the valves would be a great idea. I do think it might make your head hurt to think about it. There's lots of hoses under there.

Uncle Rog
01-21-2007, 10:50 AM
I concur, however I estimate it would take just shy of a six pack to figure it out and maybe $10-$20 in parts to do a pretty clean job. Nothing to worry about now, maybe in furnace creek in February when I will have some other help to figure it out. I will let you know if I do.....

01-21-2007, 08:31 PM
I use the suction hose to winterize but I thought it just filled up the water lines and bypassed the fresh water tank. I have never tried to fill my fresh water tank up without a hose but have wondered about this.

Does the suction hose that is located by the heater bypass valves suck the water to the tank.

01-21-2007, 08:38 PM
The suction hose will definately bypass the water heater and the fresh water tank if all the valves are turned according to the owners manuel. I dont know if there is another configuration of the valves(some open...some closed) that will divert the water to the tank. My guess is that there is as shoreline water can be diverted into the tank. All in all, it is a very good question. Like stated in an earlier response, its at least a six-pack thought process (and still will probably result in a headache)

01-21-2007, 08:41 PM
Your over thinking it. The winterizing hose does bypass the tank. But it does go into the supply system, providing pressure just like you were taking water out of your main tank. Just plug one of your outside hoses in, then stick it into the main tank fill opening. Then turn your pump on, and it will pump, out of your jug, into your standard coach plumbing, then out your hose, into the main freshwater tank.


01-21-2007, 08:47 PM
I think what Tim meant was to use the suction line on the water pump to draw the water from your portable tank, and then connect your quick disconnect hose in the docking station and run that hose into the water tank fill opening.

01-21-2007, 09:01 PM
The quick disconnect comes out at the bottom of the docking station? Then you would just extend it with another hose to your fresh water input hole. Then you would not have to purchase a pump right.