I have to install new drainage for two bathrooms upstairs, which are in a mirror layout against a common wall (tub / toilet / sink) I have the shower at 36 wide", the toilet drain is 16" from the shower curb, and the sink drain about 4ft from the toilet drain. I need help with lay out that will work with the joists that are in place. The existing dump stack to the sewer is 4" and shown at the bottom of the picture. That dump stack will be concealed within in a 2x6 wall, so there is room to work with merging pipes if need be at that wall, it will not be load bearing. The bathrooms upstairs are approximately 10x6