Unless it uses recycled water, in which case there will be a pump to fill the toilet tank from a larger storage tank. And since the pump will most likely be electric, wouldn't you need a controller to control its operation?
Something like the following, but with more features:
12 Volt Toilet Tank Refiller
It is straightforward to add a second water level sensor and a weight sensor. Don't even need any fancy logic circuits for it.

If it uses tap water that is already under pressure, an electronic control would indeed be overkill. But it is possible to adjust water level based on weight using purely mechanical methods.

I'm not sure why anyone would dislike a duel flush toilet, last weekend we installed one and it works great! it cost around $170 is a one gallon and 1.6 gallon flush, I've only used the full flush twice as the single gallon flushes solids just fine, if you are a little worried about the large amount of poop then use the full flush, if you want an even smaller flush then fill a glass from the sink and dump it in.

For that matter, I think males could use a home version of a waterless urinal?

Waterless Urinal!

Check this baby out...


Personally, I'd feel guilty, piddling in a piece of sculpture.
RVprotection Products: Thetford Toilets

But as to low flush toilets, I don't know of anything that uses less water than an RV toilet.


I've got one plumbed into my house right now, while I'm doing a kitchen/bath remodel. You'd have to go with a composting toilet to use less water.
RVprotection Products: Thetford Toilets

Regards,

-AC_Hacker