watering tomatoes in pots
The larger the pot you use, the easier it will be to keep the tomatoes happy. Unless you're growing a small variety designed for containers ('Tumbling Tom' for example) stick with a pot that is at least 14 inches in diameter. You might consider using a potting mix with moisture-holding granules (like Soil Moist) mixed in or adding the granules to your potting soil. Even with large pots and water-holding granules, you'll probably have to water daily when summer reaches its hottest.