I fill my tub up with bleach water and soak the thing for an hour then I will take an old rag or sock and scrub the dickens out of it. I spray the top with the same bleach water and wipe it down also being careful not to get the electric parts wet. It seemed to work for about 2 years then the eggs just wouldnt hatch any more. I think the bacteria gets deep in and wont come out by then. Now I am gonna buy a new one.
Remember to seperate the plastic liner from the styrofoam part when drying in the sun. Every part needs to get absolutly dry.I have some pretty old hovabators and they still work great! I also use tuffoldhens method, except I use ajax dish liquid.