I suggest grabbing a copy of the ice maker manual, most are online, and free
My ST44 manual shows the location of the pump out switch. Just like any other boat... make sure you are in a legal discharge area, open seacock, press button, hold until tank is empty. In some locations you can get in big trouble if the seacock is left open and you are in a no discharge area even though you are not discharging.
As with any boat, always a good idea to understand all thru-hull/seacock locations!