probably no worries. Pete's idea is ok, if he can find the balance. but what you want to is figure out how much water your tank "eats" in a week, and then compensate.
you gotta know your dirt, and how it looks and feels when it is in a good balance. keep track of how much water you add per week, a cup here, 2 cups there, a gallon here, whatever. adjust it up and down over the course of a month or two, and you will see that, for your particular setup, you need "half a gallon" per week (typical of what we add to our 4 ft cages, with 2 ft of soil).
i find it easier to just dump in that half gallon, or twice add a quarter gallon, than try and figure out Pete's system of an "auto-waterer" and how big that needs to be, how big the hole needs to be, how fast the uptake needs to be, and how often to refill.
do whatever you gotta do, and what works best for you, to keep your moisture content on pace. simple works best 
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robyn@proexotics.com
Pro Exotics Reptiles