REplacing a "S" Trap

I recently purchased a home and must bring it up to code. Two of the sinks have "S" traps and they are making me replace then. What options do i have if the plumbing goes straight to the floor and there is no way for a "P" Trap? I heard there was some sort of trap that will not let the water in the trap get vacumed away. Any idea if there is an easy way to fix this problem without having to move the plumbing?

The best way (right way) is to run a vent up the wall and out the roof.

The easy way out is shown below.

Depending on where you live. You might be able to use an AAV (Air Admittance valve) In Illinois I know they are not allowed to be used at all. So best bet is to call the local plumbing inspector and ask him or her what is allowed. Here is a picture to show you how you would go about plumbing it in. Also you can go to this link to see if your state approves the AAV. http://www.studor.com/approvals.htm

Aav

IT is not just the state, but some cities allow them and others do not.

To use or not use and AAV is sure to start an uproar. Some would have you believe they can be used almost anywhere and other swear they are the worst curse since the Black Plague! I suspect the real truth will never be found or agreed upon. Here's the way I see it. They are useful in some situations, but certainly not for venting every drain. In new construction, I do not see any reason to even consider them, however in remodeling there are places where when use properly, they can save the day. An AVV is a mechanical device and as such they can fail. How frequently they fail is open to debate, but because of the possibility of failure, they must be easily accessible. In the island sink under consideration in this thread, it is my opinion that a AAV would be the logical choice. The illustration by SewrzRat is how it should be installed. Obviously, you must adhere to local codes, but I think most will allow them when properly installed.