Troy - I built a tank and you can buy rubber hose (some kind of rubber) that is made just for that. Generally you can buy it by the foot. Its not highly flexible but enough to connect 2 pices of pipe.
I get mine at a local NAPA store. Most of the chain stores wont carry specialized products. But stores like NAPA should. Or at least they could order it.
The stuff comes in sizes even bigger than 3 inches. If you need bigger than that, try a supply place for big trucks.
1949 Chevy Pickup, 1929 Model A, 1962 RollsRoyce
I like showing off my personal cars. You can see my toys at:
buzztrader.com 
