From Rheem's generic Use and Care Manual for residential electric water heaters: "At least once a year, lift and release the lever handle on the temperature pressure relief valve, located near the top of the water heater, to make certain the valve operates freely. Allow several gallons to flush through the discharge line to an open drain." From a typical Rheem gas water heater user's manual: "At least once a year, lift and release the lever handle on the temperature pressure relief valve, located near the top of the water heater, to make certain the valve operates freely. Allow several gallons to flush through the discharge line to an open drain. NOTICE: If the temperature and pressure relief valve on the hot water heater discharges periodically, this may be due to thermal expansion in a closed water system. Contact the water supplier or your plumbing contractor on how to correct this. DO NOT plug the relief valve outlet." I exercise every TPR valve that isn't frozen shut (unless it discharges in a way that can damage something). I've left a few of them dribbling with a note to the homeowners to replace them (it helps to attach the note to the "routine maintenance" section of their water heater manual.) No callbacks from angry or litigious homeowners yet --- over TPR valves, anyway. Most of the "leakers" tend to slowly shut (or the rust/corrosion seals again) after ten or fifteen minutes, though. On these, I recommend replacement in the report. I do not consistently recommend exercising the valve in my report, though I usually talk about those things either during or at the end of the inspection.