Sarah,
We use 100mm underground rigid ducting, pretty well as Roy describes. It's cheaper, and easier to use, but rinse all sawdust off before putting it in the tank. Lay the tank on its side, valve down. Up to half way, it's easy. After that you have to lever the top ones up, to get others in beneath them. When full, and the tank is upright, all the pieces of pipe form a vertical honeycomb, and make very effective baffles.
Yours,
Andrew