Those large size oven bags are the hot ticket,they fold down quite small,actually small enough to fit into a Doug Ritter PSK! You can mark them with a sharpie-2 3/4" from the bottom up,That measurement comes out to 1-Liter for MP-1 tab use for purification & These bags can handle boiling water,as well! Survival Resources also has some very good bags to choose from,as well as tried/tested info regarding the large size turkey bags.It's where I obtained my info above.I have No affiliation with above mentioned products,other than being a Well satisfied customer!