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.
If the Veterinary technician knows more than the Vets change both your current ones and find one that has learnt something at University good luck.