Is that in the U.S. If so, that is probably the only drainage company in the U.S. that has the equipment to add rock on the pipe. I've noticed on youtube that it is common in Europe.
Just seen your 2 year old comment on the same subject, thought it a bit dated to warrant a reply ;-D Its common in europe, i think it allows you to use smaller diameter pipe, and it works in 95 % of soils. Im in northern Europe, precipitation roughly 700 mm, evaporation only 400 mm, we need the melt water off the fields in a hurry in the spring, since evaporation only begins properly in June . In a loamy/silty soil water will not drain well enough without a medium. In some types of clay and fine sand you're find just using a filter fabric around the pipe.
