That's for draining for winterization.
If these are bronze, tapered cone seacocks, you remove the cone from the body, lap them with lapping compound, then you lubricate them.
FYI- Groco made these wierd seacocks with a rubber cone. These have a T-handle on the end of the body to swell the cone once you've positioned the valve to open or shut. (Just in case you have these)
S/V Old Shoes
1973 Pearson 30 #255