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Old 09-26-2014, 12:31 PM   #1
Join Date: Mar 2014
Location: SoCal
Posts: 39
Fresh Water Tank Sagging

Hello - I'm looking for a second opinion on a fix for the sagging fresh water tank and water pump issue I'm having. My family and I went dry camping at Rincon in Ventura this past weekend. Between my wife and I and our two girls we ran out of fresh water, but the level check showed 1/4 full.

After looking at the bottom of the tank I realized that the water pump pick-up is above the remaining water in the sagging part of the water tank.

Here's my idea for a fix to the problem. Install a pick-up with a uniseal at the bottom of the tank sag and run a pex line to the original water pick-up right before the water pump. Does anyone think that this will not work?

I've been researching uniseal and it seems to be the way to go when one does not have access to the inside of a tank to install a proper bulkhead type seal. I'm concerned about the uniseal leaking over time with the weight of the tank and movement of the RV. Here is a source for the uniseal. Uniseal Slip Fittings For Sale

Here's a picture of the sagging fresh water tank. Thank you in advance for your input!
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Old 09-26-2014, 01:26 PM   #2
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Ford Super Duty Owner
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Location: Lowell, Arkansas
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You didn't list your RV except saying that it is an, "RV." Don't know if it's a TT or a MH.

IMHO I think it would be wiser to fix the sagging tank first. If the tank sags that much it might even pull loose eventually. I can't tell from the picture if you can easily access the bottom of the tank but I'd think a piece of 1/2" plywood braced across the bottom would take care of the sag and that would distribute the water more evenly so the pump could pick up the water.

On our first TT after we got it home from the dealer the fresh tank was sagging 7"'s. That was from the little water they used to check the water system for leaks. I read in the owners manual that many manufacturers of TT's don't recommend carrying much over 1/4 tank of water in any of the tanks. They are not usually strong enough to handle it.



TeJay (Tim) Auto Instructor 35 yrs (4-yrs USAF) Liz: RN/ WBGO 2014 Vista 30T/ F-53/ CHF/5-Star/Koni/Centramatics * Bella- Golden/Cocker mix & Louie-The cat / All Retired
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Old 09-26-2014, 01:39 PM   #3
Join Date: Mar 2014
Location: SoCal
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Thanks Tim. The RV is a 1999 Alpine MDSS Coach. I agree with fixing the sagging problem first and thought about fabricating a few metal tube brackets to life up the tank, but wood is a good idea also.
1999 Alpine Coach MDSS - 2003 GX470 Toad
Roger, Christine, Isabella(7), & Sophia(2)
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Old 09-26-2014, 02:10 PM   #4
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Location: Durango CO
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Getting the last of the water out is a pretty standard Alpine thing, that and siphoning the first 1/4 tank out when descending hills with the tank full. Here's a link to what I did to fix both issues on our '99 along with a link to takepride's original post where I got the idea.

Alpine "build thread" a collection of upgrades. (pic heavy)
The above post is just my experience/opinion which is worth exactly what you paid for it.

'05 Lance 845/'06 F-250 or '99 Alpine 36SDS Usually towing an '01 Wrangler locked on 35"s or moderate '98 Cherokee on 33"s (rear locker only)
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Old 09-26-2014, 02:11 PM   #5
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I don't know why it wouldn't work, except if it's hanging down in the space pictured it might be broken off by shoving equipment in that area. Why not support the underside of the tank to prevent sag? Plywood or a sheet of aluminum would do it. Another possibility might be to put a flexible end on the water pick up so it sags when the tank does.

Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI
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Old 09-26-2014, 03:34 PM   #6
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I think supporting the tank will fix your issue with getting the water out. I'd be concerned that the tank is flexing every time you fill your tank, eventually something is going to give like the bottom of the tank, along with the expense of repairs what a hassle. I would also be afraid that putting a hole in the bottom of the tank may give it a weak spot to start splitting.
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Old 09-26-2014, 04:56 PM   #7
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With a full tank, the 99's could siphon out a 1/4 or 1/3 of your water, makes for a short weekend. The tank on our 99 had 2 overflows. The rear was fine, it looped up behind the shower and through the floor at the water service bay, enough elevation. The front overflow comes out of the tank, takes a 90 to the side of the tank and a 90 down through the floor. A couple inches of elevation on a blotted full tank.
Empty the tank, remove the carpeted panel in your storage area to access the tank. Loosen the brackens and hangers until you can lower the tank and reach over to the front overflow. You may have to drop it completely down. Buy some pex and a basic valve. Attach new pex to the 90 at the front of tank. Run line back to the service area, mount the valve on the wall panel, then run a short line through the floor. At this point you could add a hose thread to the bottom end. Reinstall the tank, level or give yourself a slight slope to the pump. Verify that your main tank drain exits the bottom floor. This would give you a good look at adding additional brackets or supports. Although the tanks bulge, it seems like the original brackets should support a loaded tank.
To fill your tank, open your new valve, fill tank , when water comes out the new overflow, turn off water and shut off valve. You have a full tank that should not siphon. You could leave the panel off, for added storage, nail a block in there so stored boxes do not slide into the drain valve.
Alpine Coach, 2007 Apex MDT
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Old 09-26-2014, 07:14 PM   #8
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I thought about putting a fitting along the edge rather than the center of the tank but elected not to because sand or sediment in the tank will be more likely to enter the pump. With the water level up a little ways off the bottom, sand and sediment will not be as likely to enter the pump line, and clog it. I realize an input filter can take care of this problem but stuff still might enter in through overflow vents...

A filter from the tank to the pump is too much trouble.
'01 Alpine 36 FDDS
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Old 09-26-2014, 07:31 PM   #9
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I put support under mine and the tank expanded at the top instead, popping the plywood floor on the trailer loose.
The floor creaked and squeaked until I sold it.
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Old 09-26-2014, 08:00 PM   #10
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Any number of ways to support the tank sag--see forum. Might be a bit concerned that if your vent pipes arent working, you may be contributing to the sag by over pressuring the tank when you fill it. I found a short through tee for the large drain pipe at the front of the tank and was able to extend the pump feed pex line to the new tee--I just plugged the existing opening with a threaded plug. Notwithstanding the excessive sag--you are then good for the last drop in the tank.
Old Scout
2003 40' MDTS
Garden Ridge, Texas
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Old 09-26-2014, 11:47 PM   #11
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Shorty after we purchased our Alpine I had a similar problem. I also had the loss of suction when the tank was about half full while we were driving. When this happened while camping I would raised the front Jacks which moved the water to the pick up. What I did later was have a new fitting installed on the bottom of the water tank. I have not had a problem since. There use to be a tank manufacturer here in Ontario that installed new fitting for me and the cost was $10.00. They have moved I think to the high desert.
Dave Fernandez
2001, 38ft FDDS, 350 ISC, Tow 2004 Yukon
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Old 09-30-2014, 09:58 AM   #12
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Yuppie Redneck,
Follow Dave Shannons link to relocate the water pump inlet to the drain outlet conversion. many of us have done this and you get the use of ALL your fresh water. We also camp at Rincon North of Ventura and can easily stay a week. Until you get this done, you can adjust your jacks a little to move the water in the tank to move towards your current water outlet...good luck...and hopefully we will see you at Rincon sometime!!
Mike Francis and Amy Spehar
Durango, CO and Thousand Oaks, CA
05 Alpine Coach 34 FDDS Limited, 04 Jeep TJ Rubicon
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Old 10-02-2014, 08:11 PM   #13
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Thanks Mike. I will do that.
1999 Alpine Coach MDSS - 2003 GX470 Toad
Roger, Christine, Isabella(7), & Sophia(2)
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Old 02-17-2015, 06:40 PM   #14
Join Date: Mar 2014
Location: SoCal
Posts: 39
Update on the sagging water tank issue: I finally got around to relocating the water pickup to the main watertank drain and installed a checkvalve in front of the water pump. Now it works flawlessly. However, before doing the recommended fix I tried to do a quick fix by installing a pex pickup tube into the tank. That was a waste of time.

Thanks again everyone for guiding me to a solution.

1999 Alpine Coach MDSS - 2003 GX470 Toad
Roger, Christine, Isabella(7), & Sophia(2)
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fresh water, tank, water

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