Union o-ring 805-0232 fits Waterway, Aqua Flo, Gecko and Balboa 2-1/2" pump union tailpiece.
Product Note,
All o-rings are reference by part number. The size reference by the manufacturers is nominal and not actual, the o-ring will only fit a union tail piece that is referenced as 2-1/2". The actual OD dimension of this o-ring is approximately 3".