I've had no problems with mine. Avond's F-15 / Avonds pipe. Tam's smoke system.

It does put a small residue in there, but nothing apreciable in about 200 flights now with smoke. This last winter I cleaned it out, and found that there was next to no buildup, so I'm not worrying about it at all now.

I thought that in flight, it would make a more distinct 2 trails, but they mesh into each other within a foot or two behind the plane.

Lance