'used to' question tag

What the hell is a question tag?

You could say, "I used to go there?" if someone said you did but you don't remember.

You could say, "Did I used to go there?"

He is sad, isn't he? (the part in bold is a question tag)

I used to go there didnt I?

This is a question asking for conformation of the content. The context would be three friends talking.

Friend one: Did you ever got to the nightclub?

friend 2: I used to go there didnt I? (looking at friend 3)

friend 3: Yes you did and hats where you met your boyfriend.

Thanks for your replies.