You have to find the flow restrictor like Jason says. so the flush valve would go between the restrictor and the membrane.
I take it that the red line goes to drain. So after the membrane, you will find the restrictor.
Sometimes it is just pushed into the red line at the connector to the membrane.
Here is a diagram but you will have to join to see it.
http://www.reeflounge.com/showthread.php?t=2832