Our septic tank riser kits are measured by their inner diameter and height. The first number in their names is their inner diameter in inches, and the second number is their height in inches. This means that a 16’’x 11’’ riser kit has an inner diameter of 16 inches and a height of 11 inches.
The bottom ring of the riser kit is what attaches the assembly to the septic tank. There must be enough area around the access port to properly attach the ring to the septic tank. For example, a 16’’x 11’’ kit has an adapter ring that has an inner diameter of 16 inches and an outer diameter or 22 inches. That means the maximum distance across the access port must be 16 inches or less, and the top of the septic tank must be large enough to allow a ring with a 22-inch outer diameter to seal to it.
If the adapter ring is secure, it is okay for the riser system is a little larger than the hole.