How to harvest heirloom tomato seeds
Wash your heirloom tomatoes, then cut it in half across the middle (not the stem end). Gently squeeze tomato seeds and juice into a labeled glass or plastic container.
Fill containers about half full, then set them out of direct sun in an area where you won't be bothered by the ripening odor or fruit flies.
Full story: Why save tomato seeds from year to year?
Store dried seeds in a cool, dry, dark place in individually labeled airtight containers such as glass canning or baby food jars until planting time next spring.