Most old time growers still save their tomato seeds using the old-fashioned method of fermenting them. The negatives to this is the amount of time it takes (days) and the smell. If you have ever had the pleasure of smelling a rotten tomato than you know what I'm talking about.
I use the Oxiclean method. Totally safe for the seeds, does not effect germination rates and takes about 40 minutes. As simple as it gets.
1. Cut your tomatoes and squeeze seeds into a marked plastic container or cup.
2. Add about equal amound of water.
3. Add 2 Tble. of Oxiclean and stir.
4. Allow to sit for 30 minutes.
5. Before straining stir then pour into fine mesh sieve.
6. Rinse well. Put back into container and fill with water again. Let sit for 5 min.
7. Pour into sieve again and rinse.
8. Put seed on labled paper plate and allow to dry for 1 week or more. Until dry. Store in jar.