*edit* I just checked this design in all 4 directions and it worked in all but 1 direction. I managed to fix this by changing just 1 block. Look at the pic in the link below for the fix. I have also linked the test world I was using to test it so if anyone is having trouble with it they can look at it for reference. Please note that this bug can be tricky and even placing 1 block different to my tutorial can make a difference even if it doesn't appear to change any of the connections. Pic showing the fix: http://i47.tinypic.com/2vjab86.jpg World: http://www.mediafire.com/?xbkb59a26ze...
One of the most common questions on my Over-Engineering Sand Doors video was how the sand duplicator works. In this video I investigate what makes it work and how to build a duplicator.
Works in 1.2.5 and the most recent snapshot 12w21b and in both single player and SMP.
Please note: Some SMP servers consider exploiting this bug cheating, please check this before using it on a server - I don't want you to get banned.