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Old 01-25-2024, 07:27 PM   #1
rich2468
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Default Better solution for fastening Dometic Sealand 711-M28 Tank to Floor?

I replaced my recirculating Thetford Model 80 toilet a couple of years back with a Sealand 711-M28, but am finding that the 4 scrrews which fasten the tank to the floor have a tendency to back out of the floor on longer road trips.

The screws I used are the #14 x 2" long pan head screws included from Sealand with the toilet/ tank combo.

Realizing that the floor is only aluminum followed by light weight plywood covering a foam core and another layer of aluminum, I considered using longer bolts all the way through to the exterior with a reinforced plate on the outside, but the gray water tank is directly below the tank. So reinforcing from the outside doesn't seem possible.

I've considered trying to put rivnuts in the floor but I'm not sure that'd work.

Does anyone have any ideas of how to better anchor the toilet tank?

I don't have a photo, but here's a diagram for clarity.....
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Old 01-26-2024, 06:18 AM   #2
Shane826
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Even if the gray tank wasn’t under the bathroom floor you still probably wouldn’t want to go through the floor with nuts & bolts as you’d just crush the floor as you tightened the bolts.

Let me think on this for a bit. I definitely don’t have this issue on my Dometic SeaLand toilet, this is a new one!
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Old 01-29-2024, 03:20 PM   #3
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Have you thought of using toggle bolts, sometimes called butterfly bolts or drywall anchors?

Just drill the holes out large enough to insert the butterfly nuts. Once inserted into the hole, they open up and cannot pullout.

https://www.homedepot.com/p/Everbilt...E&gclsrc=aw.ds
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Old 01-30-2024, 01:36 PM   #4
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Wayne,
Thanks for those two good reasonable possibilities.

A drywall anchor should provide a rivnut-like connection with the floor without having to actually press it in place. The existing tank hold down holes wouldn't have to be increased much in size and I think (but will have to examine) that drywall anchors apply most of the force to the back side of the material (vs the sidewall of the hole).

I'm not sure how a toggle bolt would spread out within the flooring foam core. I'd likely have to increase the size of the current holes. I think, due to needing the "wings" of a toggle bolt to spread out, that a toggle bolt may be my fall-back solution.

Your ideas made me re-examine my idea of possibly using a rivnut. In looking at how rivnuts hold, it appears as though much of the holding power of a rivnut is due to the expanding of the rivnut within the circumference of the hole its placed in; with a only a small amount of lip created to prevent the rivnut from pushing in or pulling out.

Digging into the holding dynamics of rivnuts and wanting the benefits of your two solutions (more holding pressure occurring on the backside of the floor vs. the side wall of the flooring holes) has led me to plusnuts and Jack Nuts. I think that both of those ought to be able to expand within the foam layer of the floor to provide holding pressure on the top layer of the bathroom floor.

Thanks for the suggestions!





that's not a bad idea and could possibly have as much or more holding power as a rivnut.
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Old 01-30-2024, 04:23 PM   #5
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Quote:
Originally Posted by rich2468 View Post
I'm not sure how a toggle bolt would spread out within the flooring foam core. I'd likely have to increase the size of the current holes. I think, due to needing the "wings" of a toggle bolt to spread out, that a toggle bolt may be my fall-back solution.
If you use the toggle bolts (link above), Just enlarge the hole enough to push the "Butterfly nut" through the hole. Get your vacuum cleaner and a screwdriver. Wiggle the screwdriver around in the styrofoam and vacuum out the bits as they are broken up. Put the screw through whatever you want to fasten, then put the butterfly nut on the screw. Push the butterfly nut though the hole and you will hear (or feel) it open up. Even if the nut doesn't open all the way at first, as you tighten it, the "wings" will open up inside the hole.

NOW! The trick to it is that you may have to insert all 4 (assembled) bolts at the same time (before tightening). To aid in doing that get toggle bolts that are ~3" longer then the distance from the top of where the head of the screw fastens against the tank. That should give you plenty of working space. The bolts won't go through the bottom aluminum panel and having them travel through the 3" of styrofoam won't hurt anything.

Just be sure that there is no plumbing or wiring in the way.
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Old 01-30-2024, 05:54 PM   #6
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Mastik?
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Old 01-31-2024, 08:47 AM   #7
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I went through the floor, all the way to the outside, with the two bolts on the outside wall. That was made necessary last year when I arrived at the first day of a month long camping/boondocking trip and found the toilet loose. The toilet is front heavy and even though I created an epoxy plug under the aluminum skin the bolts pulled out of the brittle epoxy.

I used threaded rod as it made it easier to place the nuts on the inside so I didn't even have to remove the toilet. Once I found the long drill bit the whole job took me less than an hour, which was awesome because I was worried the trip was over, or at least complicated.

I did nothing with the front two bolts as they hadn't broken loose.
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