We Always hand scrub the outside of the gutters and downspouts during a house wash. We perform a lot of gutter cleaning in the early spring and fall, and never scrub the inside. We remove by hand the debris and clear out blockages. When possible, we also hydro-test downspouts. A penny test or a rock test is effective as well if the customer's garden hose isn't long enough to hydro-test.
Here is a recent video we produced on our gutter cleaning and gutter guard system. Let us know what you think!