How to Use the Subtract Function
1. Select the two objects you wish to subtract from each other.
2. The best way to select is to hold down shift as you click the objects.
3. Also the safest and surest way of selecting the items is selecting them by object name under Project Manager.
4. Once ready, make the object you want to remain visible on the drop-down list then click subtract.
5. View your subtracted object via 3D view and come back to step 1 for any other changes.
*Special Thanks to: TheDialux.