According to mm :

They must sell things that go on garden hoses that will mix soap in
with the water. Last year they had a product that was meant for
cleaning windows on the second floor. I think it was blue. Don't know
how well it worked on windows, let alone walls.

"Windex" has been making a hose end sprayer unit for some years now,
comes filled with the cleaner (not quite the same as standard
windex). You spray it on the windows, wait a bit, and then
rinse. Any hardware/DIY/Lowes etc store should have it.

It seems to work quite well on windows. It might work on siding,
and if not, you could refill it with something else. They're
cheap too.

Of course gardening centres are full of such devices for
spraying liquid fertilizer etc, so that'd probably work
fine too.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.