Posted: 28/01/2014 at 11:18
You're giving them Way Too Much water! My tomatoes are in large pots with a 6" gap between the top of the compost and the rim. I do not water the tomatoes until the foliage begins to flag, then I fill the pots to the brim. Sometimes they only get watered once a week, hardly ever more than twice a week. I stuck firmly to that regime last year, as advised by Italophile who is a regular on here and is a fount of knowledge re tomatoes, and had absolutely no Blossom End Rot and no blight.
Italophile can explain the reasons why this works - if I recall correctly it's to do with the plant's ability to move calcium through the tissues to the fruit being impeded by too much or erratic watering - but he'll explain better than I.