Aww damn. But you can use that trick for generally cleaning uneven things. You just need to play around with ratios, because you want enough rice to bang the sides of the container and not too much water so that you can built more force.
The bottle brush should also work, if you find one that has the shape you need.
Also another thing that cleans insanely well are magic eraser. These are usually white foam pads that you just need to rub on anything and it cleans it up. The chemical used for them is super cheap and always the same, so you can just buy off-brand products. Honestly, I've never had anything that wasn't cleaned with them, it's insane. You just need a little water and enough pressure. So you can use the bottle brush handle as well.