For right now the Porc should be OK in the 20, he will not thrive though and if you don't get him in to a larger tank soon (next month or so) you will definitely stunt him. I agree with looking on Craigslist for used tanks. I have acquired most of my tanks there for dirt cheap (250 gallon for $150). There really isn't a point of buying a new tank unless you are putting up a big display tank and are looking for specifics or special setups. Right now people are selling off tanks dirt cheap because of the economy and the cost of up-keep on these huge tanks. I had to put my big SW tank on hold for a while and went to FW. While you are on Craigs list, look for a smaller tank too that you can use for a sump and also look for return pumps and a good skimmer if you don't have them. If you don't want to Craigslist for the smaller tank, post an ad on Freecycle. Sometimes you get lucky and people are willing to give away 40-50 gallon tanks that they don't need anymore.
LGP is correct when she says that even though some people keep fish in certain conditions, it's not necessarily the responsible thing to do. The fish you see sitting in those 60 gallon biocubes will live a shorter life than if they were kept in better conditions. When you look at cases like that, sure, the fish lives for 10 years, but that only half their true lifespan of 18-20 years.
