Whats the best product to unclog a bathtub?

the only way your going to fix that drain problem is with a small drain snake. that is ran down one of the bathtubs overflows. by taking the cover off, usually two screws and pulling the stopper embly out that comes out when you remove the cover plate. then a small drain snake, usually 1/4 x 25' that you can get at home depot or Lowe's or your hardware store for around $15 and run it down the drain until the water drains. remember that you will find some resistance at about 2 foot into the drain. it is the trap that you must get past. the stoppage is usually not too far maybe about 15feet down. that drain usually ties in by the toilet. good luck