- Two 4-liter plastic bottles, like those used to sell bleach.
- 50 centimeters of tape.
- 2 meters of string.
- Four sticks, 25 centimeters long (or a box the right size).
- Some normal, woven, polypropylene sacks, like those used to sell 100 pounds of flour, rice, or whatever. Biodegradable, jute bags (like coffee sacks) can also be used and even have an advantage (see #7, below).
- A small sheet of plastic.
(Continue reading for a discussion of this system here.)