Don't mix bleach and ammonia. You said multiple but not simultaneously but I just wanted to point it out again. I am the Anti Bleach and Ammonia mixing spokesman.
>>First, wash it with dishwasher detergent. This is a very important step! Make sure you get a good lather on every corner of the tank. Rinse very thoroughly with warm water. Then you can proceed to the next step of applying a disinfectant solution (bleach, ammonia, Nolvasan, Roccal-D, etc.). Each has its own strengths and weaknesses, so you may even want to consider applying more than one solution though not simultaneously. If I were you, I would at least fill up the bottom of the tank with the solution to cover all the corners that would have come in contact with the beardie's poop, then just spray the rest of the tank with the solution. Allow it to sit 15-20 minutes to disinfect or 30-45 minutes to sterilize.
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>>It's good that you're thinking ahead rather than putting your leos in the tank. Bearded dragons maintain a variety of gut fauna that can be devastating when introduced to leopard geckos.
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>>chickabowwow
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Tim W. My Pictures
0.0.1 Leopard Geckos
0.1.0 Dumeril Boa