turn the pump off before moving touching then multi port valve, always. If you have junk or debris on the bottom of the pool, use a sump pump and not your pool pump.
turn pump off, move valve to “waste”, then turn pump back on to pump the pool water to waste. When done, turn pump off, move valve to “rinse”, turn pump on for ~30 seconds, then turn pump off and move valve back to “filter”. Then turn pump back on.
are you sure your waste line is plumbed time the sewer? Mine just come out the filter onto the back lawn.