I'm toying with the idea of finishing out my walk-in basement, but had a question about venting. The basement is "Stubed out" and I can easily see the tub drain, and toilet drain. There is a second drain in the wall behind the toilet which I am assuming is for the sink, but I am wondering if it might be the vent from the other 2 drains?

My question is, should these drains already be vented? And, is there a way I can test them before getting along further with the bathroom install? (like pour a bucket of water down them??)

Also I was thinking about installing the tub before I installed any of the interior walls in the basement so I will have room to move it around. Anything I should consider when installing the interior wall after the tub installation? The interior wall would be installed on the short side of the tub opposite the drain.

Thanks

http://img174.imageshack.us/img174/8314/basementbathroomait0.jpg

http://img171.imageshack.us/img171/9046/basementbathroombgj3.jpg