Well, does the drain pipe go down into the floor? If so, then no, you probably don't need a pump. If it exits to the sewer above the floor level, then yes, you do.
You need not only drain lines that can run 1/4" per foot down to the connection to the sewer line, but also vent lines to allow the drains to run properly without siphoning nearby drains out.
A little more info and maybe a picture would help.