Ok so this is my question.
I have seen many mods here using lots of tubing to clean the smoke. I came across one a couple days ago and they had about 4-5 tubes all connected then to the smoker. The tubes were mounted vertical. Does the smoke travel thru natural with no added fan? It seems that it would want to back feed without the help of a fan to draw the smoke back down to the next tube. Just curious on this. My mod just has the flex tube from box to smoker.
If you have ever used a hose to siphon water, you know that, as long as the "exit end" of the hose is lower in elevation than the intake, once you get the siphon started, water will flow, even if you take a piece of hose in the middle and lift it up so that it is higher than either the intake or the outtake. The gravity on the downside of the intermediate up/down section exactly balances out the upside (less a little friction resistance). Therefore, the water keeps flowing.
The same, more or less, holds true for a column of smoke. Like the water siphon, you have to get it going. If you are doing a hot smoke, the heat in the smoke chamber will help start the flow. With a cold smoke, as I found out a week ago, you may need to give it a little help. I'm going to elevate the smoker next time I do a cold smoke in the hope that convection (heat rises) will suck the air up from the mod.
Finally, as I've posted several times, I wonder the same thing as you: does all that tubing in that amazing photo of the up/down/up/down 20+ feet of duct actually do much? It sure as heck is a brute force way to get a little more "stuff" to condense out of the smoke.
Here is what I've found: in my version of the mailbox mod (see photo):
that second piece of conduit (the one that attaches to the smoker), has virtually no gunk on it, whereas the can is absolutely loaded with crud, as is the first five inches of the first conduit. I clean everything with my ultrasonic cleaner between smokes, so I can tell exactly what is going on each time, independent of what happened last time.
Having said all that, I certainly do not discount things posted by Mr. T., and I learned a lot from his posts about smoke quality. However, on this one specific issue -- which is the topic of this thread -- I have so far not confirmed that really long duct work is needed.
I have been instead experimenting with various types of metal mesh filter, inserted into the duct. My first attempt did collect a little bit of junk, but not enough to really alter anything. I am about to try a filter based on some stainless steel 3M Scotch-brite scrubbies. I'll post in my own thread if that turns out to be a good thing.
Many of the other things Mr. T. has recommended definitely do make a huge difference, including using sawdust instead of pellets; using an external box; and making sure that box stays cool.