Cheap solution to a WFP ON/OFF valve.
https://youtu.be/tNBBZHdL1q0
That certainly is a cheap solution, and well done for putting it on this forum.
However, good window cleaners earn good money (I hope you do too). We are NOT interested in CHEAP solutions. We are interested in which new ideas will SAVE us money, throughout the year. We are thinking more...long term!
We look at a problem and we think of every single inch of it. For instance, you have a coil of hose that needs to be extended and retrieved every time. The pi55ing around of that will far outweigh any benefits of your tap.
Yes the Univalve is initially more expensive, but it will become cost effective over the year.
I don't suppose you could invent an 'on demand diesel hot water system' that costs £1K , is safe, efficient to use, and does not involve any cable ties!