On planet Aquatos, You will be asked by the Plumber to collect "Sewer Crystals". The Plumber pays 20,000 bolts for each. To Receive MORE SC's FASTER, Play through, doing all Galactic Ranger missions, until you have the Gravity Boots and the Map-o-Matic, then return to the Aquatos Sewer. You may now Walk on the walls and ceiling of the Sewer like an Ameoboid. Your map also shows SC locations and most of the sewer is green. To explore the uncharted "green" areas, Run across the ceiling until you find a hole. It will take you to the Upper Sewer, with more SC's to grab. Use your map to search them out, then retrieve them. Selling SC's can get you the $$$ you need for weapons faster (I did this to get the RY3NO!).