Never had to soak mine, usually whatever is on there can be cleaned off with a brush. Soaking in vinegar will help if it is coated with coraline algae, but that is not what usually slows it down. As stated, take the cover/front grill off and then slide the impeller/blade unit out. Use a tooth brush or other cleaning brush to scrub the junk off of the impeller, blades, and inside the whole where the impeller slides into. Scrub the gunk off of the grills/housing as well. Rinse it all out and you should be good.