Clay Drain Tiles 
Clay drain tiles are orange or red clay pipe sections, usually 2 feet in length with an interior diameter of approximately 3 to 3 1/2 inches.  The 2 foot clay drain tiles are laid in a gravel bed.  A 1/4 to 1/2 inch gap between each drain tile is maintained to allow the water to enter.  The opening is then covered with a filter paper to prevent sediment from entering the pipe   Clay drain tiles were the original drain tile and were replaced by perforated plastic drain tiles in the 1970's.

Perforated Perimeter Drain Tile
Modern drain tiles are usually a 4 inch black PVC or Polyethylene plastic pipe that is perforated on only one half or side.  The perforated side is placed face down so that water enters from the bottom of the pipe.  A filter paper is usually place over the pipe or around the gravel bed to prevent sediment from entering and clogging the pipe.