I am not completely sure, but iron tanks may not be able to output steam out from anything but the 2nd lowest block + bottom. This is the case for all other liquids, iirc.
Also, I will be storing steam as I will most likely be producing an excess. This way I know when I can send the excess steam to my turbines and have that EU be gobbled up by my matter fabricator. This is also because I produce a stupid amount of biofuel and would like to maintain 100% production rates. Every time I look at my AE system and see a surplus of all this stuff that could be elsewhere, I become bothered; i.e. using up space in my AE system.