We just blew it up with lip power! If you wanted to use a pump, I would suggest the type used to inflate air mattresses. just leave inflated and hang at end of tub to store. The included suction cup hook is too weak to hold tub,Replaced it with a better hook that works well.
I just blew it up myself. It only took me a couple of minutes to blow up the whole thing. And the good news is: I never had to blow it up again! It held it's shape really well for months. I just scooped the water out and hung it up on the shower wall to dry using the attached suction cup.