You can hollow piece by using infill feature.
It will slow down slicing and increase memory usage considerably. Try use thinner walls for better performance. Infill will be applied with delay on the second pass and would appear on slice view before the second pass.
Number of layers on top and bottom of infill section.
This process extremely resource intensive in both processing and memory usage. For the better performance use smaller value.
Outer wall thickness
Width in pixels for the outer surface wall of the model which would not be affected by infill.
Pattern wall size
Width in pixels of the infill pattern walls, interior to model.
Pattern cell width
Width in pixels of the infill cell pattern.