Trouble with my pipes.

So a couple years ago Angry Bill gifted a couple pipes and some baccy to go with em. I really enjoy them and do my best to switch back and forth betwen them to give them some rest, but have been struggling with something. I get a bubling sound and feeling about half way through my bowl. One pipe is more Sherlock Holes style, though not that long, and the other is just plain old straight pipe. What is this bubbling caused from, and how do I prevent it? I am assuming it is saliva, and tar mixing. how do i stop it.

Also does anyone else get tar coming out of the mouth piece? Is this just a cleaning issue?