Adding a sink drain

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.

So does the proposed layout I've attached make sense? Will it pass inspection? Do I need to move the vent connection up to the attic?

My non-professional opinion may generate some other reponses for you. I don't think what you are proposing to do will work. Are there any other fixtures currently draining into the existing vent stack shown on your drawing? If not, then I think what you want to do is to tie your new bar sink drain into the exisiting vent stack, i.e. wet vent.

Of course, I'm not a pro, so by all means don't try this based solely on what you hear from me.

-Sam

drain

If installed as shown on your drawing, and if that is actually a vent, and not a drain for a sink on the upper floor, it will work.

They make 4" to 2" bushings. Since yr going from smaller to larger in the direction of the drain, you can use a bushing (not a 'reducer', which'd have tapered edges). If you can't find a 4x2 bushing, you can make one by combining a 4x3 and a 3x2 bushing.

I wouldn't drain into what u believe to be the vent.

See

Two responses before I could have my morning coffee. Which makes me wonder what I was thinking; I should have gone for the coffee first!

-Sam