So basically the answer to your question is “yes” you can clean a house (sort-of) without a pressure washer if you have a good understanding of the chemicals needed, and the willingness to throw in more effort and manual labour. Here is a blog I did on this very topic when my pressure washer broke mid clean:
http://www.danthewindowman.ca/blog/pickering-eaves-cleaning.html
Basically, because I understood the chems and technique, I could finish the job with an extension pole, ladders, a pole brush and a garden hose.
HOWEVER! It takes WAY longer!!!
There is a reason that pressure washing companies use pressure washers. It is the same reason that window cleaners don’t use tools from home depot.
EFFICIENCY = MONEY
While it’s possible to do a house wash with a hose and a backpack sprayer or whatever clever thing you just thought of, it’s not good enough to compete with the pros. And you won’t make much money. It might help you get started in your business if you don’t have the money to invest in a proper rig, but trust me on this: When you can afford a good pw system, you will abandon anything else and never look back.