Under most of our steam shower base/trays there is approximately a 125mm high space and a 25mm clearance from the bottom of the waste assembly to the floor. (These heights are variable depending on the height the adjustable feet are set at).
The waste from any shower needs a suitable 'Fall' to enable water to leave the tray correctly. Slow draining water means that the fall is too shallow.If your shower is located on a wooden floor or built onto a raised level, you can easily acquire the correct fall required. Where the shower is installed on a solid floor allowing for a suitable fall should be considered.
Should you have a solid floor, you will also need to ensure that a low level 'Trap' is fitted on the waste pipe.