Unfortunately, this build up is the nature of the beast. You can help the clean up by insuring that all of the metal surfaces in the cooker are "seasoned". This is done by thoroughly cleaning all debris, using a citrus based cleaner to remove all grease, and then spray or wipe on a high temperature oil, like canola or peanut oil, and then fire the cooker at a high temperature for at least an hour.
The creosote buildup may be minimized by utilizing a clean burning fire. The perfect smoke should be thin blue smoke. If you are seeing smoke that is heavier and whiter, you will get larger deposits of creosote in the cooker, and on your food.
The best solution is to stay on top of the cleaning of your cooker. A wide plastic scraper works well, but for more stubborn area, a metal scraper might be needed.
Here is the manual for the Yoder stick burners:
download/Manuals/Wood%20Manual/General%20Backyard%20Manual.pdf and here is a video on building a fire in a stick burner:
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