Cleaning Plastic Knobs. Part of the series: Housecleaning. The plastic knobs on ovens or stoves can be pulled off and cleaned with a de-greaser and a grout brush. Scrub food and crumbs off of the bottom of plastic knobs with help from a residential home cleaner in this free video on housecleaning. Read more: http://www.ehow.co.uk/video_4951800_c...