A PVC tube will work too; just remember it needs to reach all the way to the bottom and myself would drill a few holes around it, to the height of tank's drainage layer. A sponge around it will help prevent holes from clogging.
Not sure understand about the pond set-up you describe, unless it's something like this: Frog Forum - Building Dart Frog Terrariums / Tropical Terrarium Construction. If so, that will work too; but only in a non-leaking tank.