Your description on what you attend to do is not really that descriptive. But, if you are planning on working with two -basement- levels, the solution is simple. Just select a floor tool (when you are working with the upper basement), and ctrl-click (or what ever the combination to remove stuff was) on the floor to remove a tile to see to lower basement. Note that this only works inside basements. For deleting ground to have open access to a basement, you still need the stairs trick.
I undeleted this thread cause the info may be useful for other users.