Tag Question

[Grammarholic]

Can a tag question consist of three words -- after the comma -- at the end of a sentence, or does it have to be restricted to two words? Do we run into a 'comma splice' situation if we do this? Is this sentence correct? Can 1, 2 or 3 work below? Which ones are correct? Thank you in advance for any feedback.

It's really hot, don't you think?
It's really hot; don't you think?
It's really hot -- don't you think?

[Beeesneees]

The first is correct.
_________________
Cheers m' dears!