I rinse brush on, and get no problems.
Ionics multipole brush, 1.7lpm flow rate.
After the scrub of the frame, I rapidly brush one of the crossbars to get the brush a bit cleaner. Then I just rinse in a zig zag motion.
I'm a wfp noob, only done a couple of days, but this is what works for me.
Scrub whole frame first, then start at the top of the window, if seals are holding water droplets, catch the drips of the top (if there are any) with the brush, and without water flow, turn flow back on, then go twice horizontally over the top of the glass, after that scrub the window pane twice, go back to top of glass, rinse the top well, including the corners, and then zig zag down.
Works for me.