Birkenstocks are made to last. A clean sole is crucial for retaining a pair of Birkenstocks for many years. This part of the shoe becomes the smelliest the quickest. Each pair of Birkenstocks use the same type of sole, so you can clean them the same way. The easiest way to discolor the footbed of your Birkenstocks is with dirt and grass. Wash the footbed every three weeks with a damp cloth. Let them dry overnight. If you get them muddy, treat them that night with a damp cloth. Don't over saturate the footbed. You can create a great cleaner for the sole's of your Birkenstocks by using baking soda and water. Combine two tablespoons of water with one tablespoon of baking soda. The aftermath should be a paste consistency.  Add more baking soda if it is too watery.  Gently scrub the paste onto the footbed using an old toothbrush. Scrub in a circular motion and wash off with a damp washcloth. Allow your shoes to dry before attempting to clean them further. Always avoid direct sunlight for drying purposes.

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Write a summary of the previous text in Vietnamese:
Học cách chăm sóc phần đế. Thường xuyên chăm sóc phần đế. Vệ sinh phần đế bằng sản phẩm tại nhà.