Dachshund Has a Non-painful Bump at the Base of His Tail?

My 4 year old Dachshund has a bump on the top of his tail right up where it connects to his body. I'm talking about the tail that wags; not the butt. That's the only way I know how to explain it. I've taken him to two different vets. They can't tell me anything without surgery and a biopsy.

A technician working for one of the vets said she sees these all the time on dogs and they are, I think she called them cysts. She said sometimes they come back after having them removed. I know she's not a vet, but she sees a lot of dogs.

Neither vet would give their opinion as to what they think it may be. Both vets said I could have it removed or I could just watch it to see if it gets any bigger. The funny thing is, one day it's barely noticeable and like a dry spot, then a day or so later it's much bigger again. It worries me, but he doesn't act like it bothering him in any way and I haven't noticed him biting or licking it. I'm asking my Thrifty Funpals if their dog has had these and if it could possibly be coming from his diet.

By Betty