Polylok’s 500mm (20″) to 600mm (24″) adapter ring is ideal for retrofitting existing septic tanks or installing with a new tank, and can be secured with ease. The adapter ring is made of high density polyethylene. Simply fix to a concrete tank with anchor bolts and butyl/bitumen sealant (not included), then add required risers with ease.  Features of the Polylok Riser Adapter Flange Adapter ring accepts either 500mm (20″) or 600mm (24″) Polylok Risers Covers an area up to 630mm (25″) square opening Perfect for retrofitting existing tank openings Save time and money with easy installation for any DIY minded person