Putting in a a bathroom for my mom in her basement- The existing drain for the tub is 16" away from the wet wall, and 20" from side wall.... my plumber friend who was going to install it TOMORROW, SAT, said the wet wall is too far away from the drain!! Is my only option to bring the wet wall closer to the drain, and how much closer does it need to be ????? THANK YOU !! PS, going w/ a standard cheap $100 metal tub from HD (30x60x14)