Ive never understood what lads get from running pups through empty earths or pipes. I think the first time they go to ground they should mark it and enter off their own backs. Encouraging into empty places encourages wasted time running through empty spots later in their career IMO.
On a personal note I have an 18 month old dog ready to start, hes marked a couple of spots over the summer and had a couple of rags on stuff thats been dug so far so hopefully he'll be going sooner rather than later.