You start with drinking a glass of water, then you have to try to sink all the logs floating in the toilet before your stream of pee runs out. Once you sink the smaller logs, the BIG BOSS LOG will emerge.
Sink him and move on to level 2, where the logs are a bit smaller. Sink those and TWO Big Boss Logs float to the top.
Once you sink those, another round of logs float to the top, this time there a a few more. Once you sink them, the FLIES come. You now have the opportunity to hit as many flies as you can until your stream runs out. That's the end of the game.
All throughout, there's a fly here or there for an extra point.