I made myself a cheap trolley for this kind of work several years ago with a 25 ltr barrel, soon found it caused me more problems ; steps, packing/unpacking from van, narrow door ways, tangled hose, leaving tyre tracks on floors when wet etc.
was'nt very long before I bought the wcw backpack, ditched the straps , shortened the hose added a tap, carry it to point of use , is'nt that heavy and much simpler. I find 15 ltrs enough to clean the back of a 3 storey town house with.
another benefit to the backpack is if it gets really cold again this winter and hoses start freezing up, can see myself using it more to be able to continue working when I may have just given up.