Your tegu won't shrival up like a rasin, for one thing they dont gain any water through their skin.

AS for potty training you can in fact potty train a tegu. The quickest and easiest way is bath tub training. Its simple really. Everytime you take your tegu out and want to let it free roam, simply place it in they bath tub (or a tub of water in case you dont want him going in your bath). Fill it with warm water and jsut let him soak. They first few times it may take some time before he gets the idea. Once he has done his duty just take him out and let him free roam. Lizards do poop more often then snakes but this will clear his system for a few hours.

I changed this up by actully using a large cat litter box and use a all natural cat litter. I place my tegu in the litter box and he does his thing and then just wonders around my room, when he gets board or hungery he heads up the ramp to his cage and either eats or sleeps.
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Leo Gex
1.0 Giants
0.1 Red strip/hypo
1.0 Patternless
0.2 Normals
Others:
1.0 Giant plated lizard
1.0 Blue Tegu
1.1 dogs
2:0 chinchillas