Patented formula DOES NOT CONTAIN para-dichlorobenzene, a known carcinogen which is banned in ten states. Acid-stable enzymes neutralize the formation of ammonia which causes urine odors. Removes corrosion and uremic salts. Cleans, de-scales, de-limes, deodorizes, and maintains the fixture and drain lines. Round design easily fits around strainer. Last an average of 30 days.