what's the least painful way to clean white tennis shoes?

Take laces and insoles out. Warm water, a bit of dish soap or laundry detergent, scrub with a soft brush, and a magic eraser on the rubber sole edges. Baking soda paste for scuffs. Air dry stuffed with paper towel, away from direct sun - sun can turn white shoes yellow. If they're canvas they can go in a gentle cold wash in a bag.