If it's thin walled and flat, you can use electrical conduit fittings that they sell Home Depot or Lowes. Get the gray ones from the electrical dept since they are a straight thread. The white ones from plumbing are a tapered thread and you can't always tighten them down all the way.
The male would looks like this:
Attachment:
male.gif [ 3.54 KiB | Viewed 1703 times ]
) I use the 1/2" fittings, but there are several sizes larger.Also get a small tub of plummer's putty.... I bought one for 99 cents about 5 years ago....still have 99% of it left! The 2 fittings will probably cost another dollar.
Drill a hole barely bigger than the male threads in the bottom of your container. Make a small ring with the plummer's putty and stick it to the male adapter where the threads end in the middle. This will act as a seal. Put the adapter in your container so that the threads are sticking down through the hole. Tighten the female connector on the threads. Some of the putty will oose out...just remove it.
If you need a hole larger than an inch, I would recommend a realy bulkhead fitting or the uniseal.....
Enjoy!