SO! I start to fill it up. All appears well. I get about 3in of water in it. While looking in overflow, husband: "Is this supposed to have water in it?" Me: "uhh ... I'm not using a sump and have no bulkhead, so no". Husband: "Well theres water leaking into it". Me: "u've GOT TO B F***ing kidding!!!*looks in and sees small, slow, progressive, creeping of water*" So i stuff some towels in, drain the tank as fast as possible, and luckily nothing dripped out on my stand or anything. Also luckily, like any good acrylic owner, I've got some weld-on laying around. Put a bead around the bottom and on the sides. We'll find out today how well it worked. Seems reasonable that overflow wouldn't b water tight. It is supposed to have water in it afterall. Was installed later, so this is my hope.