You can use rubies to fire off pipes. When firing the pipe you will get either a driver, kart, or glider.
The total number of drivers, karts, and gliders in each pipe is fixed, and spotlight drivers, karts, and gliders are guaranteed to be included in the pipe. If you get all of the drivers, karts, and gliders in the pipe, then you are guaranteed to get the spotlight drivers, karts, and gliders.
A pipe can be reset to full again, but note that some pipes cannot be reset. (The "Reset" text will be transparent if it cannot be reset.)
You can reset the contents of a pipe you have fired off one or more times.
For more information about each pipe, see Notes and Appearance Rates in the pipe's Details screen.