If your rabbit is healthy, really never. If it ain’t broke, don’t fix it! Scent glands can get clogged up, but typically it’s linked with a health matter. Healthy rabbits don’t need it addressed.

Normally, rabbits clean it up themselves with their self grooming On the off chance you need to clean them, I would consult a vet first to ensure theres no other reason for that happening (sometimes rabbits with tooth problems will stop being able to groom properly, for example).

My vet checks Thor’s scent glands at our annual visit. Usually they don’t need cleaning I’ve been told that if they are clogged up you can tell right away because the rabbit will stink