The most effective way to clean the outside of the garbage can is to hose it down then scrub it with a brush using some multi-purpose detergent.
For the inside, if it is heavily soiled, mix a disinfectant solution and water and let the solution sit in the garbage can. Using a deck brush, scrub the bottom and sides of the garbage can. Let soak then rinse out. Let the garbage can air dry before placing a garbage bag in it.