On planet Aquatos, you have the option of collecting sewer crystals for the plumber and trading them for bolts. When you first get to this part of the game, you can go through a small area and collect crystals, but why not just wait until you get the Magnet Boots before collecting mmost of them? When you wear these boots, you can access much more of the entire area. They allow you to walk on walls and ceilings, dodge enemies, collect more crystals, and even go through hidden tunnels on the ceilings and walls. By waiting to this point, it helps you stay alive while you collect tons of these crystals to trade for cold hard bolts!