: I flushed out some sediment in our heater but no matter how tight I close the drain valve it continues to slowly leak. I noticed that the valve itself is threaded on the outside. Do I need to get a cap or must the whole drain valve be replaced and if so how? Thanks in Advance.

Martin,
Two things you can do.
Easy, get hose threaded cap with hose washer and threads and screw over the outlet. Leak stopped.

Harder, buy replacement water heater drain, and replace. This will have 3/4 pipe threads on the water heater side.