To fix a leaking plastic toilet tank, start by turning off the water supply and flushing the toilet to drain residual water. Remove the tank lid and inspect the fill valve, flapper, and overflow tube. Replace a worn flapper, which is the most common culprit, by unscrewing the old one and installing a new one. Ensure the fill valve seat is secure and adjust the float mechanism if it fails to shut off properly. For the overflow tube, trim any protruding plastic or debris. Reassemble the tank, refill the reservoir, and test for leaks. If issues persist, consult a plumber.

Leakage in plastic toilet tanks often stems from aging components like flappers and fill valves. A 2021 study by the American Water Works Association found that 50% of household leaks originate from plumbing fixtures, with toilet leaks accounting for 30% of these. Flappers, typically lasting 1-2 years, are the primary cause of leaks due to cracks or misalignment. A faulty flapper can waste 200 gallons of water monthly, as reported by the EPA. Fill valve leaks, often due to mineral buildup or a damaged float arm, affect 20% of toilets. Regular maintenance, including annual flapper replacements, can prevent 90% of leaks, saving homeowners an average of $150 annually in water bills. DIY repairs reduce costs by 75% compared to professional services, which average $200. Proactive inspection of the overflow tube, which should be 1-2 inches above the tank’s drain hole, further mitigates risks.