How do you clean a dirty gutter?

Assuming the gutters are painted aluminum, if the stain is caused by mineral deposits, an acid based detergent must be used. Proper application of the acid is a must, as well as safety clothing, eye protection and/or a face shield must be used. Plant life/foliage under the gutters must be protected along with any glass windows, because if the acid were to dry on the glass it will frost them. If the stain is organic caused by tree sap, etc. an alkaline detergent is used. Again protecting the plant life/foliage is important and eye protection should be worn. Alkaline has no ill effect on glass. Your local Hotsy dealer can help you with the detergents and applicators needed to get the job done.