I've tried the Hand Pump
on my "PUR-35" watermaker
(12VDC c/w "hand" pump option). I'd suggest it's only a "survival" device - not meant to make domestic water. Pump for ever, get very little product in return.
Most R/O units require very high pressure, so I'd be leary of the towing watermaker
. It's probably not effective.
Do you have a link to any specific product(s), I could examine?