The Amish use unprocessed milk, straight from the cow, of course they have their own dairy. So the next best thing would be whole milk, and it will take about 3 to 4 gallons, depending on the size and shape of your bathtub and your weight. The most important thing is to make sure you have your entire rectum area covered with the milk while bending your knees.
It's best to fill your tub with pure hot water and let the tub heat up, then drain. Let the milk sit until it's room temperature if it's still too cold to sit in then add some hot water but not much, about a quart.
Good luck and remember to completely relax or the tapeworm will realize it's being tricked.