Hi Fakahany,
From this site at the bottom of the page:
http://nctomatoman.topcities.com/From_The_Vine.htm
"Saving Tomato Seed:
1. Use tomatoes that are edible ripe – NOT overripe or rotting.
2. Label a Dixie cup with the name of the tomato
3. Cut the fruit in half and squeeze the contents into the cup- seeds, juice, pulp and all
4. Place the cup in the shade in a covered area outside or in a garage or shed – it will really smell bad and attract fruit flies!
5. After about 3 days, once a white fungus layer forms, add water to fill the cup – carefully remove the fungus layer and discard. Pour the contents into a fine mesh sieve and, with water running over the seed mass, press with a spoon so that everything but the seeds passes through the mesh.
6. Scrape out the cleaned seed, spread onto a labeled unglazed paper plate and let air dry in the house for about 2 weeks.
7. Tomato seeds, if stored in glass or plastic vials, will last 10 years or more, stored at room temperature."
Newt
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.