I've purchased both 33 gallon and 55 gallon bright orange bags from http://www.spectrumbagsonline.com/categories.php?cat=11 .

My kids carry 33 gallon bags and I carry 55 gallon bags - 2 bags for each person. They work well for us.

I know the local Home Depot sells clear 55 gallon bags (we use them in our barn for trash - of all things), and I've often thought they would make good transpiration bags for water collection.

Ken K.