I use a pump that I lower into the barrel and remove when I'm done thus: no fittings needed in barrel. These are available at most of the internet Fish supliers but you can also use a sump pump. I also have a heater in the barrel.
My pump is adapted to a garden hose. ( food grade, the type used for RV's available at Wallmart and most home improvement stores) Many do use fittings and permanently install pump, plumb directly to tanks etc. Look in some of the fish room posts to get some ideas. Don T.