What do you mean by spotting guys, is it when the water left on the windows drys and I presume spots?
And if you use any sort of soap or cleaner in the brush head aren't you contaminating it and waste of time using pure water?
Forget the soap IMO, its a waste of time, as in more hassle than what its worth.
Just get those frames super clean, give the glass a good going over, rinse well and you cant really have many problems.
(when rinsing, make sure you leave a inch or so gap from the top frame... this will stop any dirty drips)