Depends on your brand of water heater. Just Google "marine hot water tank parts" and go to the Defender site. They have a large selection with specs, depending on the brand. Typically 190-210 F and 75, 100, 150 PSI.
As a suggestion, NEVER flip the lever to flush the valve as some recommend. If you do, plan on replacing the valve, it will leak. Never had one that did not leak afterwards.