As the manual usually says, just the reverse of taking it out.
I lay the cross tube in loosel then the tubing and elbows, followed by the tanks.
Make sure you have the cross balancing vent tube in beforehand, the tube which connectes both tanks on top.
The hardest part is to get this vent tube and the filler tube connected and tightened withe the filler cap. Tighten all tubes and connect the fuel line to the pump next.