I've posted these pics before. I use a lobby brush on the end of a Harris pole. It's got really long bristles and gets into all the nooks and crannies . The technique is:
1 - soak the gutter and fascia etc with pure water using your wfp.
2 - give it a good brushing with the lobby brush (on a different pole)
3 - rinse off using your wfp
There are alternative methods, but this one works best for me.
Here are a few pics:
The brush (Today I use it without the jet. Just the brush on a pole. It's faster.)
A large porch being cleaned with the brush.


