Not sure how we missed this. The floors are sloped slightly toward the drain, this is how the water is removed from the floor. I hope this helps. Often We use a slot drain toward the back side of the shower but in this instance the client wanted to keep existing drain location. This was installed many years ago, the project won an award and recognition from National Kitchen & Bath in their design competition the same year it was remodeled. I hope this helps. We specialize in curb less showers throughout the Greater Sacramento region.