schnauzer bump puss filled

by Frank
(Toronto Canada)

Hi

I have a white miniature Schnauzer. Health wise she is fine, just barks a lot but I'm told that is normal for this type of dog.
Now she has a big puss filled bump on her back. It doesn't seem to bother her. I took her to the vet and he said it is a schnauzer bump and that I should bathe her more often and use a benzoyl peroxide shampoo that he sold and she would be ok... But it isn't going away.
I also read that I should use a benzoil peroxide gel but I don't know which to buy.. can you help me with that. Also does she feel pain because of it? She is such a sweet dog and very loving to the family I don't want her to be in pain.