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I find that plants do much better if you can thoroughly water them, and let them dry out completely. When they're cooped up in a watertight pot it's too easy for mould or rot to set it. And lots of my plants are too big and cumbersome to take out of the hanging planter to water every time. Drilling the pots with a tile drill bit is no big deal but I'm always on the lookout for nice new pots.
Sparky-
I must have not explained myself very well. I mean inside your waterproof pot you have a regular plastic pot with plenty of holes. The plant lives in the latter. When it's watering time you take the inner pot out and put it in the sink and water it, then put it back. No holes needed in the outer pot.
This is what I do with most of my houseplants - thought it was normal!
Edit- If you leave your hanging pots in place, with drainage holes, where does the water go when you water them?
lemonade
apc
My tip would be to use a normal plastic pot inside it and take it out to water it... unless your pots are hanging above a sink or something?