Home Depot has "Mission" couplings that have rubber bushings made to reduce one end. you will need to get an accurate OD on the large end to know what size coupling to get.
They might also have a slip on ABS reducer to go from 3" or whatever size you get when you measure the OD to 1 ½" at the small end. They just glue on. you would need some slack on the 1 ½" to get it together. Short of replacing the whole pipe, the second option would be my choice.
I wonder if the tank looks like the pipe...... just saying.
EDIT:
My bad. You would need either an eccentric coupling to fix as is, or have the ability to raise the 1½" to use a concentric coupling. Second option would leave ¾" of grey water in the tank.