In one of my 2nd-story bathrooms, there is a shower/tub combination installed. Not the 1-piece fiberglass kind, but the kind where there is a fiberglass tub at the bottom and then the wall around it is tiled for the shower.
In the room directly next to the bathroom, on the other side of the wall that has the tub/shower, I want to put in a sink with hot/cold water and drain. It seems to me that I can cut a hole in the sheetrock low and toward the faucet-end of the tub, and I should be able to see in there and tap into the hot/cold water and the same drain as the tub. But I'm not a plumber so I don't know if this kind of thing is doable or not, or if it is a bad idea or not. Presumably I can use the same drain and vent as the tub uses, but I'm wondering if the tub will flood when I run water down the sink. And since I'm not familiar with plumbing, I can't visualize what it looks like so that I know where to cut a hole in the sheetrock.