My 1977 GMC Palm Beach came with the optional Thetford Electra Magic Model 80 recirculating toilet. Initially grossed out by it, my family of 5 has come to like the toilet. The recirculating function let's us go much longer one one fresh water and waste water tank. We get around the negative of a reciruclating toilet by not going #2 in it. 

A recirculating toilet needs to be partially filled with fresh water. They call that charging it. Then you just keep adding your own waste to the toilet until the tank level is high enough (or the smell bad enough) to warrant dumping it into your waste tank and recharging the toilet. The toilet takes 3 gallons for the initial charge.

Recently our toilet stopped holding water. It was leaking into the waste tank. We couldn't keep water in the toilet to charge it, thus we couldn't flush the toilet, thus it was unsable. The problem was the valve between the toilet and the waste tank. The seal on the valve was old and had become slightly bent, thus the blade-like valve didn't make a water tight seal.

I went to order a new drain valve only to learn that they don't make it anymore. In 1978 they switched to a new seal design. My 1977 (part number 03632) has a metal top. The 1978 and newer design (part number 12836) has a palstic top and is thus taller. The two are not interchangable.

I went ahead and purchased a new style drain valve, determined to make it work. I tried swapping internal seals. That didn't work. Not all the seals were the same size. Ultimately I determined that the new valve would mount straight up place of the old one, but that would raise the height of the toilet. I 3D printed risers for the toilet feet that raised the toilet up enough to fit the new style valve underneath. It worked great. The feet raise the toilet by 11.8 mm which was the magic number to have the toilet sit stable but still make a good seal on the waste tank toilet flange. You do have to buy new longer toilet flange bolts but any hardware store has those.

The FreeCad design files (FCStd and 3mf) are available in a zip file on this same page. With these risers in place, the commonly avaialble new style valve (12836) works fine on our old toilet.

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Smll Med Lrg Berfore any mods, toilet leaks into waste tank	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg
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Smll Med Lrg Leaky valve was leaking slightly in other places too, but overall looks good for a 1977 unit	Smll Med Lrg New valve, Thetford 12836	Smll Med Lrg	Smll Med Lrg
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Smll Med Lrg Later pictures show these mounting feet better	Smll Med Lrg I made this tool to unhook the toilet from the flange for the first time in 48 years	Smll Med Lrg Its just some flat stock steal with a small hook on the end	Smll Med Lrg Made it with a bench vice and a hamer
Smll Med Lrg Worked great. Thetford suggesetd a coat hanger. Ha. Tried the hanger and it wasn't strong enough	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg RV uses a common household toilet flange which is nice	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg Notice how old valve is much shorter	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg	Smll Med Lrg Yup, this valve is 48 years old. Wow.	Smll Med Lrg
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Smll Med Lrg	Smll Med Lrg The actual toilet flange seal is interchangable	Smll Med Lrg	Smll Med Lrg
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Smll Med Lrg	Smll Med Lrg	Smll Med Lrg These feet slide forward against the bolts with nuts on top to pull the toilet to the floor	Smll Med Lrg
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Smll Med Lrg	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg I wasted time dissassembling the old valve. It was a dead end
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Smll Med Lrg	Smll Med Lrg	Smll Med Lrg Dead end. The internal seals are not interchangable. The new style is arguably a better design	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg Original screws aren't long enough	Smll Med Lrg Temporary new screw	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg I made riser feet out of plastic. Waste of time. My measurements were off.
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Smll Med Lrg Original toilet flange bolts weren't tall enough	Smll Med Lrg Got some 2-1/4" bolts then cut them down to the exact height I needed	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg I might have shortened them again after this, I don't remember.	Smll Med Lrg Damn. Plastic riser wasn't tall enough. Needed wood shims	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg Even with wooden shims it doesn't look to bad	Smll Med Lrg 3D printed risers. Green was a test fit. White should have been final but ended up being too tall	Smll Med Lrg
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Smll Med Lrg	Smll Med Lrg	Smll Med Lrg Feet were too tall so the toilet flange seal wasn 't sealing completely	Smll Med Lrg Printed new riser feet that were a few mm shorter for a perfect seal on the toilet flange
Smll Med Lrg At a glance no one would notice the height increase	Smll Med Lrg	Smll Med Lrg The 3D design showing the shape of the final toilet feet