If the player groups together biodegradable items so that they decompose naturally and smashes much of their garbage into smaller, more compact pieces, their Eco rating will rise. The scoring system is divided into two categories depending on how the player chooses to dispose of or compact their garbage to progress through the stage: Eco (Ecological) versus Ego (Egotistical). If the special trash is destroyed by accident, the player's Ego score will be penalized, and penalty trash will be released. Mottainai needs to be placed near the bottom of the trash can to be taken away by the NPC near the can. Every so often a special piece of trash, called mottainai (pronounced mo-teye-neye, meaning a sense or regret for waste in Japanese) will fall and must not be compacted (items which are assumed to have been thrown out by mistake, jewelry for example). In addition to normal trash items, at the end of every level (in Main Dish difficulty) is a larger 'boss' item that must be compacted in ten seconds, otherwise resulting in penalty trash, consisting of impossible-to-break items released into the trash can to fill space more quickly. As the trash items gradually become larger (eventually becoming whole buildings, entire pieces of land, meteors, etc.), the trash can becomes larger to compensate, eventually coming to sit on top of Planet Earth itself. Items of garbage in the game start off small, with things like pencils, pens, staplers, erasers, and other office trash. The stream of garbage will continue to drop into the trash can until either the player successfully compacts a certain quantity of items or the trash can is filled to overflowing. Players may process garbage by setting fire to burnable items, some garbage will decompose when placed near the correct substances, and lighter or fragile objects (a television, for example) may be smashed by heavier ones (a bowling ball). If three pieces of undamaged garbage fall out of the trash can, the game will end.
A stream of garbage is carried via conveyor belt toward a garbage can in the middle of the screen, and the object of the game is to break down the garbage by strategically placing it into the can based on the items available before the can fills to overflowing.