ive worked for big souless corperstions before. some pointers.
YOU cant change anything about the way things are done. If the tanks are in a real state dont take it on your self to be a one man cleaning army. and dont think its wise to ask your boss to get someone to do it. (again, they dont much like that;) )
best to just do your job, clean the dead fish out the tank, feed and clean when your told to so on so forth.
The job will be ALOT of heavy carrying too, big bags of pet food, dog beds, tank stands, displays so be ready for that.
basically tehyll tell you everything when you get a job there, dont worry about it too much. think about the staff discount (maybe get a filter like a jet engine or something lol

)
PEace out