That's a great question. I do not have a drain but I was concerned initially about this. I water the plants approximately every two weeks, (about 1 quart), in addition to the MistKing schedule. I have my MistKing come on about 4 times a day in the summer and 6 times in the winter. Twice in the morning for about 30 seconds, then the remaining times 45 seconds each. I don't rely solely on the the misters for the hydration of my chameleon however and I don't have a dripper. (Never had luck with those things). I give him water manually which is about 20% successful. I have about 3 inches of clay rocks on the bottom, fine nylon screen mesh on top of that, and then about 4" of banked soil, (substrate). I bank the soil higher at the back so that the vents in the front of the terrarium are clear. The substrate that you can find at the big box pet stores is perfect. I had a female veiled for the past two years who dug through the substrate, then the nylon screen and kicked up the clay rocks when she laid her eggs but all went well.
So not having a drain seems to be ok. No observed rot but occasional fungus which . It appears that the moisture in equals the moisture out through the absorption of the plants and evaporation. If the water level gets excessive, (only happened once), I can see the accumulation into the clay rock layer through the front glass.
When setting this enclosure up I followed the advice of an assistant professor at a university which I found online. He was very helpful and answered all my questions. He did not have drains in his setup.
Hope this helps,
Dave (Zygofeet)
