Mishnà su II Cronache 12:19

If one had left wine-jars on the roof to dry and they became filled with water: Rabbi Eliezer says: if it was the season of rain and there was [in the cistern] a little water, one may break the jars; otherwise one may not break them. Rabbi Joshua says: in either case one may break them or tilt them over, but one may not empty [them into the cistern].