My downfall as a Mater farmer..help!

[hornstrider]

I have been tomato growing for approx 5 years. I am somewhat successful, but I know I can do better. My downfall is consistent spraying for leaf disease's. I use Ortho disease control. I sprayed last night a day after a big rain , and guess what it poured down again today..I thought the rain had ended, but I should know better than to listen to the weather man.......How long do I wait to spray again?.........also I still have 2/3 of a gallon left in my sprayer.......Can I use it again??...or do I need to dispose of it after I mix it?........If I can re-use how long will it keep in the sprayer?.......I believe this might help me be more consistent w/ my spraying efforts if I have a dedicated sprayer just for Ortho disease control..........If I could just add to what is left in the sprayer each time I think I would spray more often...any help would be appricated........Thanks