It is best to use wet and forget in a backpack or pump up or pressure agricultural types of sprayers. For covering larger surfaces or heights, using the hose-end sprayer from Wet and Forget is ideal.
If you want to use your power washer, use only washers that pull the liquid from a container that has the pre-mixed water and wet and forget cleaning solution. Using pressure washers alone will not provide the right dilution, and the results you look for.