Yeah! That's what I want to do! Walk underneath a downfall of stinky muck!
On top of that, if you've ever blown out a gutter from on top of a roof, you would know that as it's working fine, suddenly there is a bunch that gets miossed, and you have to "shake it out" with the blower. The same thing happens up there with the attachment, but you can't see what you're doing. I would follow the other advice, and just do it by hand.