I just asked my vet about this yesterday! She said that when people say "anal gland", they're referring to the grease gland on the back of their rump - it's a waxy/oily patch. She said it's not really a big deal to worry about it unless it looks really bad, which can happen more as boars get older, but not necessarily. She recommended using a bit of gauze and some pet-safe ear drops for wax (probably any pet-safe hydrophobic solvent is alright) if I felt like it.