I've tried masking out a rectangle to delete a portion of the model, but it then leaves a hole, and when I dynamesh the model is reconnected between the legs and the lower back at a smooth angle again, and not with a perfect 90 degree cut out. The problem being that it's butt is a little rounded. I also have a model that is a little creature made to sit on the edge of a table or desk with the legs hanging over the side. One, even with a character design, how can I trim the bottom of an object to be perfectly flat with the surface of the floor grid so that it would sit flat after being printed? Best thing I can find is the trim tool, but that brush never seems to sit perfectly flat against the floor grid. There are a couple of problems I can't seem to figure out.

Things like glasses cases, or small, flat, hard objects like plaques or game pieces. I would like to be able to do some 3d printing of other types of objects too though. I've been watching a lot of tutorials and they are all focused on creating character models, which seems to be the primary strength of Zbrush. Edit: I ended up using the Transpose Tool to manipulate a reverse masked section as per u/DataTrek123 Thank you all for your help! I learned a lot in this thread.

Hard surface sculpting in zbrush