I used to do it that way, now I just cut a plastic the size I need, lay it on the bathroom counter, and bend over placing the piece of plastic I poured as much castor oil on as would hold. I place a light towel over the plastic and lay with a heating pad. Easy and less castor oil waste. I use organic oil. Can be costly.
Castor Oil Packs
If I have a gall bladder attack, I use a castor oil pack. I make a square of several layers of flannel (I think wool is better but didn't have a wool cloth.) and pour castor oil on it. Lay it over the gall bladder area. (maybe a 5 inch by 4 inch square?) Cover with plastic wrap. Cover with a heating pad. Usually the pain subsides in 1/2 hour. But I leave this on for 2 hours. Some say you should then rise the area with water and baking soda but I don't do that.
Sometimes Apple Cider Vinegar in water (1 T. in 8 oz. Water) will help a lot. I usually do the ACV and castor oil.
Over the years I have figured out what triggers attacks... Caffeine, dairy (except butter). If I stay away from those two things I very rarely have any trouble. If I have them once in a while, it doesn't seem to be a problem. I also only use coconut oil and olive oil in food prep and almost never eat out. (Fast food, fried food etc. Is usually a trigger for gall bladder problems. )
~Mama to Many~