how does a rocket stove maintain a constant (and safe) draft, without danger of exhaust flowing back

https://www.flickr.com/photos/smallape/3479430795/
 image of bench build
I'm not referring to the simple J style stove, I mean the kind that features long labyrinthine exhaust path to leech maximum heat from the combustion, as shown in this example.  Conventional woodstove installation places a high emphasis on ensuring a good clean path without too many bends, and even the chimney outside of the house has to be raised above the ridge of the roof, all in the name of safety (maintaining stack effect), otherwise the fire may not stay lit, and exhause can flow backwards.  How is it that rocket stoves that claim to have virtually cool output can keep flowing, why isn't it dangerous?

Re. the linked photo, that build is similar to my RMH which has 26 feet of horizontal exhaust encased in the thermal mass bench, not counting the induced drag of several 90 degree elbows, clean-out "Tees", etc. The chimney is insulated 6" ID Class-A with a height of 15 feet. There is a constant natural draft by the nature of the tall chimney, all year round, even in cold weather and when the RMH is cold/not being used. And that is the mark of a good chimney system, in my humble opinion.

Hi Yoshi, Welcome to the Permies RMH Forums!

Your question is a valid one, but not anything to be concerned with when your dealing with a rocket mass heater that produces much cleaner exhaust than most conventional woodstoves do.
Cresote can be a real problem with most woodstoves especially since the exhaust still often has unburnt gasses left and tends to collect in any area that is cool and/or at bends/joints in the piping leading to potential chimney fires.
With a properly functioning RMH,  the exhaust will be clear and all you should see are heat shimmers out the chimney stack. As long as there is enough heat left in the final vertical chimney to mantain a draft, it will pull the clean exhaust through the pipes like a train or a siphon.
To achieve this, the wood is burned quickly and at a very high temperatures vs allowing the wood to slowly smoulder at lower temperatures.

Hopefully this helps put your mind at ease and make you want to build one yourself.
If so, lots of people here to help out.
PS. We love pictures.