In another thread here where sauce making is being discussed, Brokenbar posted that to get rid of excess water in the tomatoes, she runs them through the food mill, then let the purée sit (I think she said overnight) and the pulp separates from the liquid. In case the link doesn't work, the thread is called "Lets-talk-sauce!" and it's in the General Discussion section -
http://www.tomatoville.com/showthread.php?t=29521
I know I'll be trying it next year as I prefer to cook the tomatoes as little as possible before canning, but I still want the final purée to be as thick as possible.