We power wash them using a 24ft extendable lance first, to break down the build up of grime etc. then we use a cleaning solution of water and an adequate amount of CIF to remove the black streaks. Customers Love It!
You can make up a pole like the one I did to apply your detergents to the guttering, I use this one for appliying detergents to roofs of summer houses,
This was the first one I made to apply detergents to guttering.
The forum only allows four pictures, I tried to add a picture of the trigger that controlled the flow of detergent.
I don’t use any of them now as I use the lance with a pressure washer to clean inside and outside of all guttering.
Very inventive Jeff.
I have similar for those larger awnings 
I use the F13 and the green synthetic brush that is sold at pressuretek as well. That brush is unreal compared to the best brush you can get at Lowes. I would have never guessed that there would be that big of difference in brushes but there is. If someone has never ordered from pressuretek then it is well worth your time for power washing stuff to check them out, BAR NONE they are unmatched in service. Bob(the owner) is a ex window cleaner himself.
Didn’t knew that about Bob.
I’ve bought from them before and never had to talk to them, but I only hear good things about their service, and that’s good.
BTW, Jeff I’d love to see more pics of that device.
It can be really useful around here. Could a ball valve do the trick since you have the trigger open all the time ? or a trigger itself can be mounted in-line ?
