Yes, sandpaper works really well to clean a toilet, but you must be very careful so as not to scratch your porcelain. Select a fine-grit sandpaper, wet it thoroughly before use, and scrub carefully and gently. Wear protective gloves, avoid using it near the rim and inner bowl, and test it in an inconspicuous area first. Overall, it's best to use a toilet bowl cleaner specifically designed for porcelain surfaces and a toilet brush for scrubbing.