The Rhino I OFS is a Heavy Duty Sch. 80 drain used as an Overflow Bottom Drain together with a vertical riser or as a Sidewall Return. This drain is also available with the standard cover plate. With the standard cover plate installed, you can convert back and forth between a standard drain and an overflow drain. Simply remove the cover and screw a 2", 3", or 4" riser pipe into the internally threaded drain flange. Here again these drains are constructed of the same Sch 80 heavy duty material as the other Rhino drain models. A bottom drain can be said to be one of the most important parts of a pond installation, in that itís integrity is paramount to the success of the entire project. Compare the engineering of Rhino bottom drains to any on the market, and you will see the evident quality.