Venting of basement plumbing fixtures
In short, yes, you need to vent every fixture. ALL plumbing fixtures require venting. The sizing and location of the vents is determined on the specifics of your layout. So without seeing detailed drawings, I can't say. But everything will need to be vented. Check if your local code allows mechanical vents. They are either known as Air Admittance Valves or Automatic Air Vents. They are little one way air valves that you essentially attach along the drain line and don't require you to run vents up and out of your house. Most national codes allow them, but certain town overrule and don't allow them. My town is one example. My town uses the 2006 National Standard Plumbing Code, which allows such vents, but my town doesn't allow the vents...go figure.