What I have done in the past was to spray the entire leaf surface with a soap solution of about 1 teaspoon Dr. Bronners in a quart of water, then blasting it off a few hours later with a hose or sink sprayer, I have even used the showerhead before. Be careful not to spray down into the pot and focus on the undersides of the leaves to dislodge and survivors. Repeat like you would neem oil.