Medium gravel provides enough weight for your piping, while allowing the water to flow without taking the gravel with it. Pea gravel and oversize gravel are also available if you would prefer smaller or larger gravel.
#10 limestone and red sand are your options.
We recommend using CR610 limestone. It is a blend of fine gravel and a powder bonding agent. Over time, the weight of your car, coupled with the occasional rain, will help compact it into a nice solid base.
A ton of gravel will cover approximately 100 square feet, 2 inches deep.