I do my ferrets at nail trimming time, I use slightly warmed (tepid) water on a cotton tip
and wipe the crevices of their ears on the outside of the ear, 2 to 4 cotton tips per ferret.
Some people use mineral oil, baby oil or Olive oil. What do you use ?
If their ears are dirty or have ear wax build up you will need a ferret safe ear cleaning solution.
Loosen any wax or debris by putting a few drops of ear cleaning fluid in the ear (warm the solution in your hand first), massage gently around the base of its ear then clean with a cotton swab and wipe away any excess.
Remember ...only clean as far as you can see! Do not push the cotton tip in the ear canal, you might pack the ear wax in tighter or worse damage the ear drum.
and Dont reuse cotton tips or swabs on other ferrets, incase of spreading infection or ear mites.
Please Note : If your ferret's ears have a dark wax, are smelly or have coffee granule type dirt he needs to see the vet as he may have and ear infection , ear mites or both.