Having another look at the photos..
It seems like only part of the original bowl is missing, could you make the missing part out of Fibreglass so it fits to normal pipe?
You could use compressed air to operate a pneumatic piston that pulls the plunger on the syphon.
Keeps electrics away from the water and would probably be able to set it up to use dual flush
You can use a pump to flush, I've done this before on tempory/hire type toilets.
Just a push button activating a timer to run the pump. No cistern involved.
I've even done short & long flushes on the same push button.
I was using 12v pumps and the flow was a bit lacking but you could easily use...
So, if the equivalent of 2.5nm is 254gm..
(Ie, a 254g weight on the end of a weightless 1m long tube)
If the arm weighs 100grams, what's the maths to work that out?
How close would I be by taking off half the weight of the arm?
Ie guessing at a 100g arm with 204g on the end of it?
If you buy 8mm Hex you don't need a lathe, you can make them on a pillar drills.
Center up the first one then clamp the vice to the table and clamp in a bit of bar as a side stop.
Make them as long as the drill/tap will allow for then cut them down after.
If the Hex fits in the drill chuck you...
Although,
I have a torque screwdriver that goes that low, 2.5nm would be a one-handed twist probably less than it would take to drive in a small wood screw with a regular screwdriver.
Compare that to holding out 2.5 bags of sugar at arms length...
And my arm is not a meter long...
2.5kg...
Actually, try and find a "crowfoot wrench torque caculator"
IIRC mounting a crowfoot on a torque wrench backwards/inline with the handle results in you needing to set the torque wrench higher than the final torque achieved.
You could easily make up a "crowfoot" style wrench by filing a...
Alternatively, make up some sort of leaver arrangement to reduce the force of the 5nm torque wrench by half.
How accurate do you need the torque to be?
254g/m
But, you also need to account for the weight of the arm.
And, the arm weight won't be applying as much force nearer the bolt as it will 1m away.
There are maths to work that out if you fancy doing it.
Maybe take half the weight of the arm off the weight on the end and hope for the best?
Another option,
What are the dimensions of the brackets?
How many do you need?
It might work out cheaper than the fuel cost to have them made and posted to you
Have you got a friendly aa/rac driver?
They carry the midtronics testers that will diagnose it with no risk of damage.
A load tester may well finish off a bad cell although to be fair, if it dies under load test, its not any good anyway!
The only time I have seen anything written off on a farm is when they have borrowed a bit of machinery from a mate and damaged it.
Seems to be farmers code of honor that you have to replace old with new if it's damaged so they usually just put in an insurance claim for those ones..