I cleaned my car mats that had coffee stains, cola stains and dirt on them by filling my large deep sink and putting Mr. Clean in and letting them soak. After a while, I took them out and washed them off with a hose outside on the driveway. They came out beautifully clean.
Try using OxyClean. You don't need to soak and wait. Just a tablespoon or two of OxyClean, then brush for about 1 minute, then wash away with a hose. The whole process takes about 1 or 2 minutes.
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