When you say ripples, do you mean a pebble grain surface like it comes from the factory or true ripples from heat distortion or some other defect? I take mine to the 25-cent car wash (it's actually $1.50 to start it followed by quarters to extend the time).

I start by soaking it with the engine degreaser/tire cleaner selector. Then I scrub it next while on the foam brush selector. I finish with a good rinse. I'm careful not to apply high pressure to the seal where the top meets the lower half or any other spots where the water doesn't belong under pressure (fridge and water heater vented doors, furnace exhaust, other seams, etc.). That's just me though. If your ripples are damage, I would not follow my suggestion since you may cause more damage.

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