Perhaps if you put the lid back on and cut holes only big enough for them to feed through (a couple of inches). This should stop them from sweeping their heads back and forth.
I got mine from ebay. They seemed to be the cheapest.
http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=150613416537
50 pack for 7 bucks plus shipping
It is always a good idea to keep buckets of water away from chickens. Especially for small young chickens. We lost a 2 week old chick that way. On the up side it does kill a lot of mice.