A washing machine discharges water water at a very high velocity and high capacity. This is far more waste water than the pump was designed to handle. The washer discharge must be connected to what's called an "indirect waste", that is, it must discharge into a laundry tub or sump, so that the excess can be stored until it can be taken by the pump. The specific code that governs this is in chapter 27 of the International Residential Code.

Also in the manufacturers instructions, they allow the discharge from a washing machine ,through an indirect waste. [sic] "The Sanivite is a drain pump that is ideally suitable for use in a basement apartment or anywhere in the house where additional fixtures are most wanted. It will pump waste water away from a variety of sources such as: a kitchen sink, laundry sink, washing machine ***(indirect connection)***, dishwasher, bar sink, etc."

This pump will never be able to handle the discharge directly and you need to provide a receptor to accommodate a washing machine. Is there any possibility of adding a laundry tub adjacent the washer and Sanivite pump?