See this is why I wished we lived closer together. I have a special tool for Those odd and hard to reach Nuts. It alows you to Change the angle, and Still retain a goodGrip in order to Break Free Just about any Kind of Not and or Bolt assembly.
It's Hard to do with Pliers, or Vice grips, But This Thing ould do It in a matter of seconds.
Just be glad you don't have to Replace the Wax Seal. If you seat the uhm Seat wrong, You'll have a major Sewage leak, and have to Buy another one.
Stephen