[morticaixavier]

A 2L yeast starter will add 1/2 gallon

only if you don't decant!

[bboy9000]

I have a an 8G stockpot and have no trouble getting over 19L in the fermentor as long as I don't boil the living crap out of the wort.  The wort needs to be boiling, not jumping out of the pot.  I get it to a nice gentle boil for the first 40 minutes then turn it up a little if I need too.  It also helps if I use pelletized hops instead of whole hops.  Yes, I'm starting with a slightly larger pot but I usually end up with more beer than I can fit into the keg.