I don't use a backpack and my aquatec trolley gets me most places - but steps and locked gates are fun with 50kg (2 barrels) of water, a pump, a 15kg leisure battery, pole and hose.
My longer hose has sorted out most problems but one conservatory clean was fun as it was further from the car than my hose would reach and up about seven steps - here's what I did.
Took battery and pump around to conservatory, took 25litres water (good barrels, grip at top and finger holds at bottom so can carry twohanded) by hand, connected up - did whole (v small) conservatory including roof - algae - the lot. Back to car 45 minutes and £30 not bad when eighteen months ago the roof alone took me that long before wfpole and pure water.
Backpacks - must weigh at least 25kg full up with pump and water - or hold less than 20 litres? - wouldn't want to carry that weight when I could push twice as much or more on a trolley.