In-tank toilet cleaning tablet

They are commonly used to prevent toilet bowl stains from calcium, limescale, mold, etc.

It is originally invented by Flushco, Inc. in 1978, branded as 2000 Flushes (acquired and now owned by WD-40 Company[3][4]).

[5] Eventually, some other brands and companies such as S.C. Johnson Scrubbing Bubbles,[6] Clorox,[7] and Ty-D-Bol sold their own in-tank toilet cleaner tablets.

[8] A major complication that may occur includes bleach breaking down rubber gaskets and corroding steel parts.

[9] Another issue is the blue dye commonly used in in-tank cleaning tablets may cover up iron deposits.