I prefoamed the center pipe to make sure that it stays put once I foam under the tank. I also wanted to be sure that I could pull the center pipe out before the tank was installed. It worked as planned.

Notice also, the vertical tubing that has been inserted into holes at the outboard end of the laterals. The vertical tubes have been greased and taped to the floor. They will be pulled out after the tank has been foamed in. No matter how high the foam rises on the sides of the tank, there will be holes thru the foam to allow any water that gets into the bay, out into the bilge.