The Advanced Insertion Pipe is an intelligent pipe. When connected to a container (such as a Chest, Furnace, Macerator, etc.) it will only insert items in the container as long as the container is able to accept items. If the container cannot accept any items, e.g. because it's full, the items will continue on another way, however, it will not go back the way it came. If the Advanced Insertion Pipe is the last pipe in a connection, and the item is left with the choice of either going into a full chest or back the way it came it will still pop out. To prevent that, there must be a second pipe attached where the items can continue. The Advanced Insertion Pipe will only connect to Stone Pipes, as opposed to Cobblestone Pipes.