Wonderful system, isn't it? I really appreciate mine.
The draw is substantial. Sanitizing is done by in effect "blasting" temporary chlorine out of sea water or salt water, using an electrode system. Their website is at raritaneng.com, and owners' manuals are available there. Unfortunately the LectraSan manual there does not show total draw, but it must be under fifty amps (@ 12 volts) as the three fuses total that. My manual for an old old old system does show the actual draw, but I do not have access to it right now.
Basically, there are two motors and one electrode pack. It's the electrode unit that has the biggest draw. The motors and pack would be pretty easy to amp out while they are running.
Easier, Raritan's customer service by phone is fantastic. From NZ suppose you'd rather not, but try email, can't imagine it's too much worse. They can give you draw to the amp. Note draw can vary somewhat if the seawater isn't at least above a certain minimum salinity. If it is not, the electrodes will draw a little more, but this isn't a common situation, except perhaps in brackish coastal areas, river mouths, etc. It will also actually drop if you allow the unit to become dirty, etc.
I actually have not seen Raritan claim that the new units drew that much less. For your demand calcs, you also need the cycle times and those are in the manuals. Bear in mind that none of this includes any draw from the toilet (if electric) and its macerator (if any.)
Any other questions, ask. | 
