I saw that! Good looking riser tube, and it appears to be about 24" long? I'll check out the south east US refractory suppliers and see what I can scare up. That monster batchbox you guys built is something else. Peterburg dropped in a post over at Permies, including the brick layout, lots of photos and other details. I'll include the link here for others that may be reading this thread:
http://www.permies.com/t/40007/rocket-s ... Innovators
An old house was being demo'd just down the road, and for several days was open for anyone to salvage anything they wanted. There was an old rusted out wood fired funace in there, and I salvaged the cast iron doors with mounting flanges! I'm thinking 6" batchbox now:-> Either that or use the doors for cleanout access to a bell style bench.