I purchased my current home six months ago and it was clearly plumbed for a basement bath when it was built in 1997. In the corner of the basement there are three PVC pipes sticking out of the floor, one 3.5in, two 2in and a stack about 8 feet away. The largest of the three is the toilet and I assume the other two are the sink and shower. However, how can I determine if these were vented when installed?