OH... and before you cut your rain barrel....read my assessment of using them in winter. Don't want you to go into it without knowing that you might HATE it in winter...
http://naturalchickenkeeping.blogspot.com/2013/02/poultry-cup-drinkers-waterers-winter.html
http://naturalchickenkeeping.blogspot.com/2013/02/poultry-cup-drinkers-waterers-winter.html