Years ago I installed a Thetford Curve (550E) toilet, and very shortly after I installed it, I noticed the flushing switch would get a little finicky. The toilet flushing is operated by a motor powered by 6 AA batteries, to allow for portable use, and it started getting to the point where, at every trip, I'd have to pull out the batteries and reseat them, as if there was corrosion at the contacts.
On the last trip where I did this, one of the battery contacts just fell out -- it had disintegrated over about 6 years. It wasn't a huge deal since you can "flush" by simply dumping in some fresh water, but there was no way to access the water in the toilet's fresh water tank.
I long ago wished there was a way to hard-wire the toilet into the TM house battery, to skip the whole AA battery problem, but this was the impetus to make it happen.
And so, I:
- removed the lid and seat. To do that, gently back the right side of the switch/water tank lid out of its hole (you'll bent it slightly when you do this, but doing so doesn't deform it), which will then allow you to pull it out of the left side and completely remove it. When you do that, the lid and seat are released and can just be lifted off.
- unscrewed the cap/battery tray from the toilet
- ripped out the battery tray
- ripped out the circuit board, to which the micro-switch controlling the flushing was mounted, and, according to web searches, was also subject to corrsion and failure. Replacement "battery packs" apparently cost around $100.
- cut out a 1/2" hole in the remaining cap, where the switch button was, with an exacto knife, as well as removed some of the structure under the cap that held the battery pack that was in the way of the nut for the new switch.
- mounted a new push button switch in the hole (https://www.amazon.com/dp/B07T11VYHV)
- connected a barrel plug to the switch, and routed it out the left side of the cap, so that the wires would fit in a slot made in the left side of the male threads of the pump housing. In hindsight, it would have been better to route it out the right side so allow for better clearance with the seat and lid, but that would also require cutting a new slot in the male threads of the pump housing. Either way, I don't think it's a big deal.
- wired a $9 DC/DC converter to the old Thetford Electra Magic wire I had left in there, which has a 12VDC input and a 9VDC output (corresponding to the 6 AA batteries at 1.5V each) (https://www.amazon.com/dp/B00A71E52G)
- wired a barrel jack to the converter
- connect the toilet flush motor to the switch and power. Normally, the motor gets power from the battery pack via the 2 metal tabs at the top of the motor housing. The plastic holder for those tabs just pushes out of the side of the motor housing, which will reveal the wires leading to those tabs. Just cut the wires. On mine, red (at the back) was NEGATIVE, and blue (at the front) was POSITIVE.
- connected the plug to the jack, and presto, unlimited flushing. When emptying the toilet, simply disconnect the plug/jack to allow for moving the toielt.
Since the circuit board provided for "controlled" flushing, where, no matter how long you pressed the button, it only pulsed the pump for 1-2 seconds, the operation is now such that it will flush for as long as the button is depressed. Not a big deal, but we will have just have to go easy on the flush water.
If you're not already having problems with your switch, you might consider removing your switch/battery pack whenever you're home. I've also read that overfilling the water tank, whatever that means, can short out the circuit board.
Pictures below!
Dave