If you are in trouble because your park is literally covered by trash, you can use this little but useful game bug. You have only to save your game, then load it again. All the trash will magically disappear from your park's path. Of course this won't solve the real problem: too many trash and too few cleaners at work. You have to fix the problem by yourself.
If you want to buil a long and complicated roller coaster, or another type of free track design ride, but you don't have enough cash to do it, this little game but will surely be of great help to you.
First, you have to build the entrance of the ride, and the shortest, simplest track you can build. Then open the ride (paying only a few money) and immediately close it. Now demolish the ride except for the entrance (you have to leave it). Now build another track, long, complicated, exciting as you want. When you will open the ride again, you will noticed that you paid only the fisr short track, and the new amazing track is not totally free! Same if you need to modify the track another time, you won't pay anything. Happy gaming!