Plumbing Questions? Ask a Plumbing Expert.
A washing machine or Automatic Clothes Washer requires a 2" drain pipe. It is likely you do not have that size. This is NOT the size of the discharge hose that connects to the machine. The drain pipe is what the discharge hose dumps the water into. That must be 2" pipe.
If you had a previous machine that discharges slower, or less water, you may have been OK. The best solution I can give you is to install a laundry tub. As a laundry tub is large, it can act as a holding tank for the discharge until it can drain out of a smaller, 1 1/2" drain.
Before you do that, you should talk to the manufacturer. Restricting the hose size may damage the pump. Additionally, be aware that less volume = higher pressure and you may still have a problem. If you're going to restrict the hose, do so close to the unit so the high pressure will lower with more volume. Meaning only restrict the size for a small portion.
I am not sure. What you need to do is contact the manufacturer. I doubt there is anyway to reduce the flow rate. Maybe having a technician come and rewire the discharge pump for a lower voltage.