If anyone is considering building a sprayer the attached link has lots of tanks that might work well and the price looks decent.
<A target="_blank" HREF=http://www.usplastic.com/catalog/product.asp?catalog%5Fname=USPlastic&category%5Fname=Polyethylene+Tanks&product%5Fid=Mix+And+Fill+Tanks>http://www.usplastic.com/catalog/product.asp?catalog%5Fname=USPlastic&category%5Fname=Polyethylene+Tanks&product%5Fid=Mix+And+Fill+Tanks</A>
<A target="_blank" HREF=http://www.usplastic.com/catalog/product.asp?catalog%5Fname=USPlastic&category%5Fname=Polyethylene+Tanks&product%5Fid=Mix+And+Fill+Tanks>http://www.usplastic.com/catalog/product.asp?catalog%5Fname=USPlastic&category%5Fname=Polyethylene+Tanks&product%5Fid=Mix+And+Fill+Tanks</A>
