jsl,

How do you expect to fill the 50-gallon drum? Is the tree somewhat near your house? There is a system you can build. Google rain-barrel drip system. It will irrigate very slowly because the pressure in the line is very low. A tree only needs water when its being established so look at something that is temporary. Usually these systems are DIY. There are many past threads on these systems. Let us know what you expect to pay for a system. We can help you with ideas. Aloha