I would like to add a bar sink in my basement, but I'm having trouble figuring out the best approach. As you can see from the diagram I've attached, the main drain pipe for the house comes down right were I'm putting the bar, and there is a vent stack (presumably for the floor drain) right next to the main pipe. My question is, can I tap right into the main 4 inch drain pipe about 18 inches from the floor with a sanitary T, reduce it down to 2 inches, and then use that for my sink drain? Of course, I would still have to tap into the vent somehow. do they sell 4" to 2" reducers? My other thought was to knock out the concrete and tap into the main pipe under the floor, but I don't think I would gain anything by doing that. My main fear is that I will end up with a sink full of sewage everytime someone upstairs flushes. Am I over-reacting? Thanks in advance for any comments.