Ditto Maryann's Ditto.
In 35 years of horse ownership, I've cleaned two sheaths, and I've owned geldings longer. My first horse rarely, if ever, needed his cleaned; I think the equine dentist did it once or twice while he was sedated for dental work (he was 27 years when he passed, I owned him for 24 years). My gelding with Cushings was the first sheath I ever cleaned myself, and I attribute his dirtiness to his metabolic condition. I do have one now that will probably need to have his cleaned more than the previous and other, 7-8 boys, I've owned over the years; he doesn't drop to pee much, so likely to get more dirty than a gelding that drops more to pee.