Clean the toilet - look under the edge with the mirror
Clean the toilet, where necessary, without much chemistry, but with an overview. With mirror around the "corner look" or look under the edge.
Just under the edge of the toilet bowl hide stubborn coverings, it can do nothing toilet duckies. The toilet brush with "under the edge part" tries everything possible, but somehow the nasty rubbers manage to hold themselves there, because one can see them badly. Keeping your head deep in the pottery, turning left and right and risking a hair wash is not everyone's cup of tea.
For a specific basic cleaning just hold a small hand mirror under the edge, you can already see where a thorough scrubbing is necessary. With discarded scotch britt or something similar, scouring powder and gloved hands, no problem getting everything right.
Is only really bad the first time. If you think reasonably regularly then it's easier.