How does the fabric softener dispenser work in my washing machine?

No the spinning cup flings the liquid to the side, there are non visible holes near the top of the cup.

We don’t have running water so the pressure is too low to hook the washing machine up to the tap, so we just stick a hose in the center cup and close the lid to fill it for a cycle or rinse. The water comes out the holes and into the machine, the cup will not overflow.