I'm also interested in how small the smallest amount of wort is possible with the 50L with standard malt pipe.
I believe the short malt pipe does 20L batches, but I'm curious to know how little liquid is required to create a sufficient flow for mashing. Perhaps 30L batches might be possible?
I asked the same question on another forum from a user and this was his response:
You can make a 5gal batch but the malpipe has to have at least 8-9kg of malt in it so the beer will be strong. You could buy a smaller maltpipe for the 50l. I did but have only used it once..