hi all. hope this helps. sometimes when you get birds muck which is hard to get off EVEN after leaving to soak with the water when wfp. i found a tip which helps is to tap your brush on top of it (careful though with fragile or weak panes)
as the bristles splay out they tend to remove even the most stubborn birds muck . i thought i would share that with you as it works every time when i use that method
regards tomo