I have studied to take my pesticide exam and will take it when my local extension office is open (next week or maybe not until after new years). I have been mowing for 5 years and decided to get into spray applications this year. I would like some advice on choosing a sprayer. I like some of the ideas I have read about having a large tank- say 200 to 300 gal. (with only H2O, or do you mix your potash and other chemicals in it too?) with a smaller tank (50 gal or so) to make custom applications (for insecticides and pre-emergents, etc). What is the cost on such a unit? Do you custom build them? Can I buy a 200 gallon skid and weld a platform to it with a 50 gallon tank and plumb them to the same pump, then open valves to select which tank to use (am I oversimplifying this- I can do plumbing, but have never done a spray tank- is there more to it than that?) Also, what are good brands? I have looked at the Lesco skid. I don't mind buying used- more money in my pocket. Any suggestions? I will be doing foundation spraying too, but plan on using 4 gal. backpack sprayers for that.