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Defenestrator 09-20-2020 08:15 PM

Do not overfill Bigfoot freshwater
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Learn from my dumb. Turns out, running to do something else while the black tank drains and forgetting that the freshwater fill is also running can have consequences a lot more severe than just a puddle. I think I've distorted/mangled the freshwater tank and probably broken the mounting, plus damaged the underbelly cover.

Vent tube screen blew out (easy fix, back in place already)
Vent tube and fill tube leaked a bit from top attachment (easy enough, just loosen hose-clamp, re-seat, tighten)
Bottom panel distorted. Might pop back into place once the pressure's relieved, but I'm not optimistic. Likely will need replacement, which will be a pain (looks like about 100 screws, some of which are stripped)
Tank mount probably busted. I assume it's a metal strap that'll need to be replaced. Hopefully no damage to anything more permanent.
Tank busted. It still holds water, but the pump sucks air even when the sensor says it's 1/3rd full. I'm guessing the bottom is now round rather than flat, and possibly other sides as well.

On the plus side, looks like I'll be installing SeeLevel sensors and maybe heating pads plus more insulation.

South Coast Stu 09-21-2020 11:48 AM

What year and model? Looks a lot different than mine :confused:

Defenestrator 09-21-2020 11:50 AM

It's a 2019 25RQ. I think they've changed the details on the underbelly coverings a few times over the years.

South Coast Stu 09-21-2020 12:14 PM

Interesting. The water tank on my 2003 21RB sits on the sub-floor (in the rear of the trailer). It is inside so it's protected from freezing (assuming the inside is kept above freezing temps).

On yours it looks like the water tank is forward and sits on the fiberglass shell belly itself?

Sorry to hear of your trouble :(

John in Santa Cruz 09-21-2020 12:15 PM

I've always filled the water tanks on all my various trailers right up to the overflow vent, never had an issue.

Defenestrator 09-21-2020 12:19 PM

Up to the overflow vent is fine. It's rapid sustained filling beyond that that's the problem. I think the flow rate was too high and pressure built up. The tank isn't strong enough to take the weight of water plus extra pressure.

John in Santa Cruz 09-21-2020 12:37 PM

ah. I usually leave my 60 PSI regulator on the faucet end of my white water hose, that modulates the fill rate.

Defenestrator 09-21-2020 01:06 PM

Yeah. In this case I was filling up at home, so I skipped the usual regulator and filter. I figured it's not a sealed system anyways, so overpressure just means a little spilling. Turns out the fill hose wedged into the spout surprisingly well, and the vent tube probably can't keep up once it fills with water.

Rzrbrn 09-21-2020 04:44 PM

I have a 19 25RQ and am very interest to see what the underside of your trailer looks like and what need to be done to fix your issues. Please take a lot of pics and post. Hope all goes well.

Defenestrator 09-25-2020 10:25 PM

4 Attachment(s)
Since the bottom's distorted, I figured I'd start off to the side. Less risk of the tank popping out with force when the panel's removed, plus I'll likely have to remove the valve cover anyways to get the second panel off.

Turns out, there's a small access panel above the axle that was overlapped on top of one of the valve cover screws, so step zero was removing that. The panel gets you access to the cable-operated (no wonder it's kind of a pain) black tank valve and what looks like the shower drain (though that doesn't reconcile well with what I see looking down the drain).

Defenestrator 09-25-2020 10:33 PM

4 Attachment(s)
Prepping for valve cover removal. Lots and lots of sealant to cut, and some digging needed to get at buried screws.

The low point drain valve handle pops right off then it can be pushed into the cover out of the way.

The black handle unscrews, then there's a bolt with a lock washer. Once those are removed, the black dump cable attachment can also be pushed in to get the cover slide off.

Defenestrator 09-25-2020 10:41 PM

4 Attachment(s)
Luckily for me, there's no screws and little to no sealant in the part of the dump valve cover that's tucked behind the frame.

After all the hidden screws were removed and I used a razor to cut through the sealant, I worked a short prybar around the edges until it came loose. A putty knife would probably also work well here, and I've been using it with good results elsewhere.

Defenestrator 09-25-2020 10:46 PM

There's an absolutely massive amount of sealant in places. Especially around where the main cover meets the little square cover that's actually attached to the piping.

Insulation is fairly minimal. There's maybe 1" of EPS around the edge, but the bottom is just a single layer of reflectix. Hoping to improve this to some degree, though there's less room under the tanks than I thought because the bottom is convex rather than flat. I can at least improve the area around them, and there's definitely room for heating pads both on the tanks and on the dump piping near the valve. This'll keep me from needing to run the furnace so much, which is handy since I'm full-timing and often have hookups.

Defenestrator 09-25-2020 10:59 PM

4 Attachment(s)
Couldn't get a good photo, but I at least learned that the tanks are mounted on frame crossmembers near the top and the freshwater tank is still in place, just bulging. Which means it won't fall on me when I remove panels. The panel's thin plywood bonded to fiberglass so it's likely just pushed out of place and not permanently damaged. There's a board along the seam between panels that's clearly being bent. May have to replace that.

I'm not really sure how to remove the tank once I get it opened up - it almost looks like it was dropped onto crossmembers from above before the floor was installed, and "remove the entire interior and floor" is definitely going to put this in "find out if insurance covers it" or "hope the freshwater tank is merely out of shape but still intact enough to use" territory.

Lots more screws buried in sealant.

Several bent screws, and one sheared off. The sheared one is blocking panel removal and I can't find my extractor, so I've ordered a set. In the meantime, I can clean sealant off and unscrew the second panel.

Glenn Baglo 09-26-2020 12:10 AM

Are you sure the tank is deformed? Maybe that's the design and build.

Defenestrator 09-26-2020 12:49 AM

Well, there was a loud bang and now the entire underbody is somewhat convex instead of flat like it was before. The gray and black tanks are a half-inch or so above the bottom cover panels. The freshwater tank is visibly pushing downwards on the board below it, to the point that it's sheared a couple screws off and distorted the edges (see various photos). It is definitely a good 2" taller than it was before. So, yes, I'm sure.

I think the ridges/creases in the convex bottom allowed it to bulge outwards. If it's in good enough shape and I can't easily swap it out, I may end up trying to just re-shape it. Heat it up somehow to 150F-170F or so somehow, plug the vent hole and attach a vacuum to the fill hole to create a small pressure difference, and push upwards gently. Might pop it back into shape if I'm really lucky. Really not sure how to do the heating, though. It'll need to be reasonably uniform and hot across a large area.

PatD 09-26-2020 02:25 PM

Elliott, don't hesitate to write Bigfoot, mines a 2008 and they always get back to me.

They'll want to know if they can improve that issue. They do have the warning on the filler cover not to fit the fill hose tightly on mine. pd

Bruce Olive 09-26-2020 04:23 PM

The “underbelly” panel on my 2018 25RQ was slightly convex the day I took delivery when it was brand new.

Daniel W 09-27-2020 06:55 AM

Defenestrator...Thanks for the very detailed posting with pics. Helps me understand the underbelly tank set up on my 25RQ.

computerspook 09-27-2020 01:34 PM


Originally Posted by Defenestrator (Post 794021)
Up to the overflow vent is fine. It's rapid sustained filling beyond that that's the problem. I think the flow rate was too high and pressure built up. The tank isn't strong enough to take the weight of water plus extra pressure.

OK I have a 16 foot scamp and there is no way to pressurize the fill. But I do have to only fill so fast so I have a short hose I built to do this. On the end that screws on the main hose I replaced the rubber gasket with a circle the size of the O of the gasket of old intertube I have cleaned. Then I put a bit less than a 1/8 inch hole in it. That limits the speed to what works well with the tank.

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