Sight glass seal leak on old pressure tank

[CharlieNH]

I have an old galvanized pressure tank at our summer camp, where we drain the water each winter. What kind of sealing set-up am I likely to have on the sight glass, which is leaking at the bottom seal? I've been reluctant to get into this for fear of breaking the sight glass or having trouble replacing the seals. Looks like compression nuts at top and bottom. Does the sight glass have a lip at the ends. Are these easy to find if anything goes wrong? Thanks for any advice about what to expect.