From recollection I just went for a standard size close to the one quoted. Not important as you can always fill in with silicone sealant, which is what is recommended.
However, personally I would not bother with the smell and coating due to using a SOG. All toilet fluid is now biodegradable so a SOG is no longer needed.
Use chemicals and avoid the stench.
Gerry
However, personally I would not bother with the smell and coating due to using a SOG. All toilet fluid is now biodegradable so a SOG is no longer needed.
Use chemicals and avoid the stench.
Gerry