40 plant hydro system
 

Ron -

My friend asked me to build a 40 plant hydro system for his wife, and I've never made one on this scale before. I was thinking of making a 60 gallon tank by connecting 2 30 gallon rubbermaid containers together with PVC, but I don't know what kind of pump to use. How many GPH should it pump? Is this too big of a tank?

I wouldn't use two tanks. You can buy a very large container at any large home improvement store or I also have used a 55 gallon plastic drum turn on it's side and cut a hole on top. You can also used trash cans like I did with my first large garden.
I have used 55 gallon drums for as much as 150 plants. I also had to fill it ever day though.