Bleach is heavier than water . When you pour it into a full, clogged toilet bowl, it sinks straight to the bottom. Instead of mixing with the clog, it sits underneath the water. The clog floats on top of the bleach, untouched. You then flush, and the bleach rushes out first, leaving the clog behind.
Bleach is the only "cleaner" that makes a toilet dirtier (by destroying the glaze) while trying to unclog it. Use a plunger or an enzyme drain cleaner. Never bleach. will bleach unclog a toilet
Before you pour bleach into a backed-up bowl, consider these serious risks: Bleach is heavier than water