Will this product clean black lines in a toilet bowl?

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Our product works most effectively if our product can adhere directly to the affected stained areas undiluted. If you have hard water buildup or a stubborn looking stain below the water line, the best way is to remove the water from the bowl (either physically or turn the water valve off located behind the toilet, flush it then plunge out any remaining water). If stains are above the water line there is no need to remove the water. In either application: Apply the CLR directly to the stains using a damp cloth or sponge, take a stiff bristled brush or a pumice stone (sold in hardware stores for toilets, it’s compressed lava, needs to be run under warm water to moisten first and is safe enough not to scratch the porcelain), and scrub for no longer than 2 minutes gently in a circular motion. Flush to rinse. Repeat if necessary