Capstar is amazing. We use it on the foster cats we get when they have fleas.. Within 30 mins you can see the fleas 'abandoning ship'. I treat them in the bathroom so that way no fleas get into my carpet. It only treats adult fleas though so you have to give them something to treat eggs and larvae too.
My parents dog had a very similar lump at the top of her tail, mum got it checked out and it was just a fatty lump. She had to have a skin cancer removed a few months later so they also removed the fatty lump while she was sedated but it would've been fine if they had just left it there.

I'd definitely take Tambo to the vet and get it checked out - better to be safe.

Cute name by the way - I have a friend whose dog is also called Tambo and another friend whose cat is called Tambo too.