[Sal]

When sowing tomato seeds you will usually get several sprouts in one pot. Once they reach a certain size with a couple of sets of leaves, just pop the ball of soil out of the pot and crumble it until you can separate the plants and pot them on into individual pots.
When separating tomato plants from a ball of soil, gently crumble away the soil (sometimes a chopstick or other dull implement can be useful in this exercise). Then, handling the plants by the top leaves and stem, gently try to pull them apart from each other. Try not to touch the roots. I don't think submerging them in water would be necessary and make sure you don't over water when you first replant them. Good luck!