1 1/2” (37.5mm) Septic Stone is a washed or dry screened clear round stone, ranging from 1” to 1 1/2”. Commonly used for Septic System Drainage, or Roofing Ballast Stone this material also serves the purpose of a Small Riverstone for decorative features in gardens or around the house. Due to being free of any dirt or small particles, it also makes for a great drainage stone, which can be specified for use in infiltration galleries, and other water features.