This Flange Adapter Plate is the perfect piece to install underneath the OGO Origin toilet directly above a toilet flange. It enables you to plug the flange and quickly fasten down the plate to install the OGO. In RVs, this allows the OGO to be installed right above the original black tank without having to remove it. 

https://learn.ogotoilet.com/how-to-install-rv-flange-adapter-plate