Dan.... the process is a very simple one..... its just we that like to make it all voodoo complicated
Make or buy the water
Get it into a tank
hook up a pump/battery to the tank.... outlet from pump to hose connected to your reel
Connect your pole hose via a connector normally rectus 21 or 26 for most people to reel hose
Water up through hose in pole to brush head... now just scruba'dub'dub'
Agitate dirt, rinse off.
I used a freedom trolley for about 2 years, first with 25litre containers then added a 250litre tank, used trolley as the pump/controller... Went to 650 litre tank to 400 then back to 650 now going back to 400litre tank. I think alot of people prefer 500litre tank size... I'm sure they'll chip in and elaborate.
Some people use a pump controller, some don't....horses for courses..... you can make a setup as cheap or expensive as you want but at the end of the day we all just pump water from a tank up a pole and out of a brushhead.... its that simple.
Please forgive if this comes across as condescending, its not meant to be...just trying to say its very simple but I do understand how at first glance it can all look at bit complicated.
if you are able to connect a few hoses, using very basic handtool skills then thats half the battle.
If I were you...put a shout out to see if anyone would be willing to actually show their setup.... you are more than welcome to come here but.... but it'll take you a few hours as I'm near to the Dutch/German border.
tips...if your serious.... skip the backpack route, they are a nice tool but I would hate to use one all day every day, but saying that a few people on here have done so for extended periods.
Get a good pole... I am biased... Gardiners SLX-25 for me all day long... but plenty other poles available.... get a decent lightweight brush-head.
Cheers Dave.