Per Guv Bob:
I might (not saying I would - just might) consider drilling a 1/16-inch breathing hole, and when finished pouring the water out, I might thread an eyebolt into to it to seal it up

Couple days ago, I received 5 of these: http://tinyurl.com/llec2lf

They seem to work - with the caution that you need to use a conventional
high-speed drill bit and not a spade bit. Get a hunk of similar
polyethylene and try the drill you are going to use first.
--
Pete Cresswell