That valve is a S2020-1, which supersedes to S2020-2, which then supersedes to S2020-3. The S2020-3 is ~$40. The CCA-2900 is Curtis's non-OEM direct replacement and is ~$22 (they also make the S2020-3 for Cessna). Unlike some other drain valves, this particular drain valve is non-serviceable, the o-ring is inside the stem and that stem has a rolled over end, so it cannot be accessed to replace. I don't recommend attempting this as owner preventative maintenance for a couple reasons... 50 gallons has a lot of head pressure and it's going to be coming out with some pretty good velocity also the tab for safety wiring the valve is very thin metal, so it's very easy to tear through it if you aren't careful. And that tab is riveted to the bottom skin of the wet wing, so replacing it is no fun. Of course draining the tank can make it a lot more of a non-event, but where is the fun in that.