An odd couple that solves a real problem: Ronco's 8 inch inspection lid with a black collar and a clear lid. The black collar belongs on holding tanks; the clear lid is for the moment after a rinse-down when you want to verify the tank is actually clean - proof through the lid, without re-opening a port you just sealed. Maintenance crews on rental and fleet rigs specify exactly this combination for exactly that reason.
Eight inches is full arm access, the size that makes interior service - retrieving a dropped tool, clearing a blockage, swapping a sender - possible without pulling the tank. If a tank gets one port, the argument for making it this one is strong.
The collar is installed on your tank at Ronco's Tustin, California plant when ordered together, placement coordinated with the rest of your layout, per-order as the company has built since 1974. It belongs on tanks from the RV holding tanks range and the boat tank line alike; browse the Ronco Plastics hub for the rest.
OneSource Plastics is an authorized Ronco Plastics dealer.