Hey, I'm cough cough American, and I'm in here right now doing internet searches for alternatives to toilet brush. I find them so ick, and yet have always had one. Now, i have a new toilet- taken from a Palm Beach mansion, no less, and it lacks flush power. Requires 2 and 3 flushes to clean at times.
I'm thinking that leaving a gunky toilet would embarrass my guests. For myself, I pour water against the bowl to clean if needed, and I use brush in a clean bowl for routine freshening.
I found your discussion while looking for ideas of what to leave for guests that would be easy and not gross them out. I assume anything at all would be welcome to avoid the embarrassment though.
I am embarrassed by the horrid public and political behavior of at least a third of my compatriots. Maybe it is these who travel to your B&Bs because some of them had no compunctions about relieving themselves on the floor of the capitol building.
I've seen a thing called, "Shifter" which sprays water, but it's only available in U.K, I think. Nevertheless, probably anything which can crate a steam of water will clean the toilet bowl.
I won't apologize for my compatriots as I have no association with these types.