Dear Christian, Gnatterboxers,
The majority of my existing smoke deployments used Seuthe smoke gens, either 501 or 503 "bottom feeder" units. I run them at 1/2 the rated volts or less, thus eliminating the possibility of "dry boiling" the gen to the point of destruction. The lower "oil cracking" voltage also affects the smoke ejection velocity. The result is a far more gentle "wafting" effect as opposed to a visibly vicious "blast" of smoke.
Using bottom-feeder gens allows plumbing of remote oil tanks, to ensure sustained oil supply in mission-critical and marathon show deployments. (One of my earliest smoke-gen deployments was a small Seuthe #22 gen in the vertical boiler of a HO sawmill. That was a top-loader, and I learned the hardway that having to constantly refill the tiny built-in 3ml reservoir got old very quickly, particularly under show conditions!).
What to plumb the tanks to the gens with? Well, rubber RC car/airplane fuel tubing. Mounting the tank at or slightly above the level of the gen ensures the system is "auto-priming".
I use Seuthe smoke oil exclusively. Mixing Smoke Oil types and thicknesses can encourage clocgging of the gen, which can be a pain to rectify. Some modellers use baby oil, as is is significantly cheaper than Seuthe or other "model smoke oil". However, baby oil is comparatively _very_Thick_, and is virtually guaranteed to clog most gens if the gen is left to cool down with oil still in the chamber.
In terms of $$$, one of the other benefits of running the gens at 1/2 volts is that you use far less oil! I buy Seuthe oil in 250ml bulk bottles, and such a bottle tends to last me more than 3 years of regular show service...
I do have 2 X ultrasonic "water atomiser" foggers salted away, which were intended as "drizzly rain" gens for my current HO street switching layout. However, while the gens worked a treat standalone, they:
1 - used water too fast
2 - couldn't be easily controlled such that the water level was maintained at "optimum" to give the best fog-conditions
3 - weren't compatible with any known form of dispersion system that would give a wide constant "drizzle" without re-condensating the fog back to totally out-of-scale water droplets
(ask me how I know this...)
UltraSonics actually get a good wrap with the RC boat crowd,
as "fuel" for the fogger is plentifully available...
BTW, apart from the out-of-scale water droplets,
and the risk of soaking layouts and structures that are not adequately prepared, designed, or constructed,
the water vapour emitted as fog by the ultrasonics is pure H2O
(any chemicals or impurities are seperated at the point of fog creation).
This is interesting, because as shown on a previous edition of Carl Arendt's Scrapbook, it is possible for mechs to run in such "pure water" baths...
Anyway, I hope this helps. More info available if required...