I made my own sauce with canned whole tomatos once. I put the whole tomatoes in a blender and blended till it was a sauce. Then I poured it though a 6" strainer with holes around a 1/16 of an inch or less. I had to push it through the screen a little with a plastic spoon, took a few minutes for a 28 oz. can of tomatoes. Most or all of the seeds were left whole by the process and were left in the strainer, but 99.9 % of the red stuff went through. Not sure if this is because I have a weak blender or the setting I had it on, (the fact that seeds were not crushed) but you may want to experiment with a few tomatoes, a few blender settings and a couple different strainers if you have them.