We are looking to install a washroom (toilet and sink) in our basement. There is a rough-in for the toilet - black pipe with cap- but no other pipes visible. Our home is about 5 years old, and this was installed at the time of construction.
We have been told that in order to vent the toilet and sink, a pipe has to be installed that goes all the way up and out our roof. The concrete is still intact around the rough-in. Is there the possibility that the venting hookup is somewhere in or beneath the concrete floor? Also, since we can't find any piping in the walls that could be venting for the sink, can the sink be vented from the same system as the toilet - if this is present?

If there is no venting system hookup, would the new venting system have to go all the way up to our roof, or could it be vented at ground level, which is several feet above the floodline of the toilet and sink that are to be installed.

Many thanks for any advice!

"We have been told that in order to vent the toilet and sink, a pipe has to be installed that goes all the way up and out our roof. The concrete is still intact around the rough-in. Is there the possibility that the venting hookup is somewhere in or beneath the concrete floor? Also, since we can't find any piping in the walls that could be venting for the sink, can the sink be vented from the same system as the toilet - if this is present?"
If there isn't another smaller pipe to plck up the lavatory that will vent the toilet also then the plumber didn't leave a vent and cement will have to be taken up to cut in a 2" lavatory drain and stub -up.

"If there is no venting system hookup, would the new venting system have to go all the way up to our roof, or could it be vented at ground level, which is several feet above the floodline of the toilet and sink that are to be installed."

If you're asking if you can terminate a vent in the basement the answer is no, however, if local codes allow you may vent your syatem using a AAV, Air Admittance Valve) cheater vent,(see image).
Good luck, Tom