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&amp;category% 5Fname=Polyethylene+Tanks&amp;product%5Fid=Mix+And +Fill+Tanks>http://www.usplastic.com/catalog/product.asp?catalog%5Fname=USPlastic&amp;category% 5Fname=Polyethylene+Tanks&amp;product%5Fid=Mix+And +Fill+Tanks</A>