I'm interested in this one as well. Our limited experience:
We've drilled holes in the head of our barrels the size of a stainless steel part that we have off of some other bits in the brewery. It is effectively a stainless 'nail' that we are able to pull out to sample. Be careful drilling holes...we have some that are too tight and some that are too loose, causing them to leak.
What we are thinking of doing on the next go around is to drill a hole and fix a 5/16 stainless tube (using a corny dip tube) into the bottom of the head. We will then be able to put a John Guest on/off valve, using for sampling and also to quickly be able to hook up to pump the beer out when it is ready.
Jeff Rosenmeier (Rosie)
Chairman of the Beer
Lovibonds Brewery Ltd