Muriatic acid is best for removing stubborn toilet bowl stains - silive.com
TOLEX Strong Toilet Descaler
Muriatic Acid - How to Use Muriatic Acid
Chem Clean Limited - Chem Bowl is a very effective toilet bowl cleaner formulated with 25% Hydrochloric Acid. It quickly eliminates uric acid, iron stains, lime scale deposits, rust and foreign matter