There’s two types of preening for volans: general preening, which is done twice daily, or thorough preening which is usually once every few weeks.
General preening is a quick once over done twice a day (like brushing hair.) This kind of preening is very casual and doesn’t involve more then a comb, water, and maybe some kind of product (oil, shampoo, whatever. There are salons specifically for this kind of wing care.)
Thorough preening is what the name suggests: a thorough cleaning of the feathers. This kind of preening takes longer and is not done in public, as it is considered an intimate bonding experience reserved for family, close friends, and partners/lovers/insert relationship here (this will vary volan to volan. It can also be done solo.)
Volans with fangs are able to use their teeth for the process. Some prefer it, some don’t, and some reserve it for specific people or do it only for themselves.