Blanktanks are oval containers just big enough to fit a bean inside. Two blanktanks are kept empty inside Professor Garbanzo's Fix-It Shop until needed. They are used to heal injured beans. First, they are filled with chow by dipping them into the Chowdown Pool, or by making chow inside of them. Then it is opened from the top to put a bean inside of it. Inside the blanktank beans are surrounded by chow and sleep the entire time they are in the tank.
In vol. 1 Beanish (as a chow sol'jer) got a krink'ld leg in a chow raid and was put in a blanktank. Following this, Beanish broke out.