David,
I think you might be wasting your money.
You don't need to be 'tied to your bucket'.
Why not carry a couple of bottles of Fairy, but filled with your cleaning solution?
Just squirt some solution onto your applicator when it dries out.
Refill them with water from a customers tap. There'll be enough soap left on your applicator to cope with a good few dousings of tap water.
I know a window cleaner who only carries Unger Gel (a soap you apply directly to your appicator) and a couple of bottles of water which he re-fills from customer's taps; no bucket.
I imagine anything which involves a bottle and a tube to your applicator would be a pain in the rear to use.