A dry pit is constructed as above. The two pits should be next to each other, and fairly close to the campfire and kitchen area. For the dry pit you simply need a 'hole-in-the-ground'. Only place thoroughly washed or burnt material here, otherwise you will have animal visitors and insects paying you a visit, making life in camp a bit more uncomfortable! 
Never place any glass or sharp materials (e.g. a ripped tin can) in the pit.
When you have finished with the pit, it should be filled in with earth and completely covered. It should then be marked with a sign placed into the ground at that point with a date on which it was created.