Rain gauge cache
A Rain Gauge Cache is usually a micro container placed within a long PVC tube tied vertically to a tree or post. At the bottom, the tube has a screen or a plug with holes in it, on which the actual cache rests, and which allows water to drain. In order to retrieve the cache amd to sign the log, the cache hunter must plug the bottom and fill the tube with water to make the cache float to the top. After signing in, the hunter allows the tube to drain and drops the cache back in. Of course, the cache and its log sheet must be of a water-resistant variety.