Baby anacondas can actually be quite shy.. a 55 gallon tank is really huge for a baby.. you may have trouble getting it to eat. Something along the lines of a 10 gallon tank (or better yet a plastic tub) will be better for a young snake. As it gets older and more confident/settled in, you can move on to the 55g tank.

Are you getting a male or a female? Adults will need either a 4'x2' cage or a 6'x2' cage depending on how large they are.. females of course are considerably larger, but anacondas are slow growers.