Flush with fresh water for about 5 minutes. Why waste the expensive salt-away product, because if you keep running water through, you are washing the product out, once the little dispenser cup goes clear. You don't need a sump pump, the dispense cup works fine. So, flush the hell out of it with fresh water. Then, for the final 2 minutes switch to the salt away product, and run it briefly. This way, the product is left behind to do its work, which is actually providing a protective coating which builds up over time. Makes sense, does it not? I have been doing this for over ten years with my 2 Yamahas and they are not worse for the wear, so it must work. Plus, I had a chemist cousin who worked for Dupont "keeping the world safe for democracy" if you know what I mean, who actually did some research on this about it leaving a protective coating behind, with continual use. But if you simply flush until the cup runs clear, and keep flushing, you are defeating the purpose of the salt away product.
What you will see coming out of the back is bubbly water, like soapy water after you have washed the dishes.