I just use my fingers too and give them a good scrub during a bath. Someone suggested baby wipes. I thought that sounded a lot better then the stinky fingers method
I always use my hands also. Sure you could use baby wipes, a wash cloth, an old rag, a soft bristle brush. But you can't get at it the way you do with your fingers.
Excaliber works great for cleaning between the teats as well the "boy parts" I always use hat with a washcloth whenver I bathe my mares. It works good and doesnt leave any residue that sop can.