A coat of the new white spray paint for plastic (Krylon | Krylon® Fusion for Plastic®) on the outside helps maintain low water temps in the bucket (and reflect light).

I drill a hole (1") in the base, and use spigots from home brewing (beer) buckets, attached to a hose, for EZ draining (see spigots: NORTHERN BREWER: Fermenters and Accessories). Rigged-up irrigation valves never held a seal, and leaked for me. These things are the right tool for the job.