Charles…What is the 4 cast iron pipe ?? Is it a vent pipe ? Is it a soil pipe ? Is it vertical or horizontal ?You really need to know what the pipe is before you connect anything to it…for instance..If the pipe is a soil pipe for a bath room on the floor above, and a toilet is flushed, there is the distinct possibility of having raw sewage coming up in your new deep sink. If you are sure that the 4 cast iron pipe is suitable for your intended purpose, the pipe can be cut with a Wheeler or Ridgid ratchet cast iron pipe cutter. Insert the appropriate fitting at the proper elevation, and secure in place by using fernco couplings. …Lots of luck with your project….Bud.. Suncoast Plumbing Inc. Sunny Florida..: How do you go about tapping into a 4 cast iron waste pipe to add a deep sink?? Thank you for you help in this.