Why do toilet suppliers caution against over-tightening the nuts on toilet tank fixtures and trim? Last Update: Oct 02, 2002

Toilets are made of vitreous china, an exceptionally strong and durable material but one that can crack if subjected to a sharp impact or excessive stress. Rubber or plastic connecting washers on most fill valves, flush valves, and trip levers are designed to protect the china. Installers should use care not to over-tighten all nuts. Plastic coupling nuts, if over-tightened, present another problem. One toilet manufacturer cautions about the risk of external leakage as follows: "...If over-tightened, a plastic coupling nut may crack, resulting in water leakage. Failure to use a brass coupling nut may void [the manufacturer’s] warranty.