Basically, there are two types of used barrels that you will find. Ones that have screw off tops (thus usually handle dry type goods) and the ones I have (which have fixed lids that are melted onto the barrel)
Now the reason for the large holes. it goes like this: I bent my brain trying to figure out how to drill the spigot and overflow holes and then cap them from the inside. There is no way to do it other than cutting an opening in the lid. Since I'm 6'2" and 190 pounds, I had to make the large so I could fit inside to cap the spigot hole at the bottom.
Also, bug control. if you have water barrels or any standing water for that matter (especially in the summer) and don't want to take daily malaria pills (although gin and tonics will also work), you can get these little donut type deals from Home Desperate that hold a dormant bacteria that once activated, go after the mosquito larva like they were popcorn. I highly suggest them, that is unless you enjoy itching your skin till it bleeds. Everyone needs a hobby. ;)
So there it is. If you have any other questions, please write, I do respond to questions, because I need something to continually boost my ego. :)