To install a new bathtub on the second floor with the drain down & in between the floor joist, will i have to open the ceiling below or can you usually reposition till you get it?
I installed a tub a couple years ago, and I think you will need some access. I was able to open the floor on the opposite side of the wall, but if your drain is on an outside wall, I think you will need to open the ceiling.
Good Luck - Tony
It can be done but it requires some very careful measuring. You have to install the trap and tub waste so that when you install the tub in the opening it drops right onto the tub waste. Your last connections are the overflow face plate and the tub shoe. It would be much easier if you had access from the back or below the tub.
There has to be access. Even if you could position the drain, trap, flange and overflow the the gnats @55, you would never know if it was watertight without a visual (until it was too late). The "easy way" is to work backwards from the tub drain, which requires access at least from the wet wall side, below is not a necessity, or else you could never have a tub on a slab.
We do it on slabs all the time. To check for leaks you can see the trip waste and trap by looking behind the head wall from the tub side. What we do use is a glued PVC trip waste. In this area it's called a rapid fit tub waste. Most of the tub used here are builders grade. There steel tubs that rust out after 10 to 15 yrs. We must replace six a year, and were are a small company. ( father & son ) I should say just son I retired this year.