I don't have one either, but I read a lot and am very spacial/mechanically inclined. True, you cannot usually pass a pipe cleaner through them while assembled because the pipe cleaner is more prone to follow the "system" cavity in the base of the stem. That does not mean that once it cools down it cannot be disassembled and cleaned similarly to any other pipe. I am sure a couple of vets will chime in here. But really the only difference from what I see is that you might require a doubled up fluffy cleaner or swab to clean out the "system" cavity of nasties. The theory being that the moisture can condense and drop down into there instead of being in the main bore of the shank/stem causing gurgles or sour condensation to enter your mouth.
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On my Systems I remove the stem and swab the well with a paper towel/napkin or a couple Q-tips if handy. Clean the stem and airway as you would for any other pipe. If you do this after every smoke, no need to clean "while" smoking.
Can you use a retort on these?
On a related note, can you use a retort on a p-lip? I assume it would be hard to keep the tubing from covering the hole.