In article .com,
says...

My house was built last summer with drains prepped in the basement for
a bathroom; a toilet and sink drain were placed and the concrete was
cut where a shower would be placed. What will I need to do to connect
to a vent for the sink? How difficult is it to install the trap for
the shower? Finally, if I connect a second sink for the bar to the
drain for the bathroom sink, how should I connect the vent?


For venting the sinks: after the trap on each sink, the drain pipe will run
back horizontally, usually into the wall behind the sink. At that point it will
turn down to connect to the waste system. Place a sanitary tee at the point it
heads down. The down leg goes to the waste, the up leg is the vent. It must run
vertically until it is 6" above the top of the sink. 42" above the floor is
usually specified. Then it can turn horizontal to connect to the existing vent
stack.

Here is a great forum for plumbing advice, read through the old posts, there
are lots of questions answered and photos posted:

http://terrylove.com/forums/


Dennis