wfp is the best thing ive ever done for my business danny.nearly 2 years wfp now.DI vessels are not that expensive.buy a new one!
have you got tank,pump,controller,hose reel and pole?
get a 25ft SLX as soon as funds allow and an aqua-daptor and give yourself 6 months to get used to wfp cleaning.change all you work over to the pole straight away(tops only)then slowly clean most bottom windows over the next few months.
you will be SLOWER than trad for the first month or so but you will speed up over time.as for work being easier youll be able to get more work cleaned in a day but youll still be knackered when you get home!!

best wishes
dazmond