In the UK, in some cases, you can use an “[air admittance valves][1]” for a toilet, rather than a vent pipe provided you have a stack between it and the public system.  

The ideal is that when you flush, a “surge” of water goes down the pipe. The air in front of the “surge” needs to be able to escape out of the way by going up the stack, and air must be able to get in behind the “surge”.

Check if your local codes allows such a setup.


  [1]: http://en.wikipedia.org/wiki/Drain-waste-vent_system