1. use a diamond pipe and direct the cobble into a void pipe.
2. use a diamond pipe and direct the cobble into lava.
3. use a diamond pipe and direct the cobble into a cactus.
or
4. use a diamond pipe and direct the cobble into a long ass cobble pipe feeding right into your neighbors sorting system, maybe they need some cobble.
Personally, I'm a big fan of 4.