Hey Tom, 4" square sounds like a tall order to me, but I live in the Caribbean and 3" square is quite popular for guttering and can usually be purchased from any hardware.

If your local hardware can't help you, I'd say check hydroponic suppliers online or in your area.

I just started trying some hydroponics and I used 3" round PVC. I am regretting that now because personally, the round pipe has too water reservoired in it. Afterwards, I thought to myself that since I am trying to this long term, I should spent the extra time and money to get proper equipment.

Thanks Egas! I've decided to go the international route & am sourcing most of my components from China! I'm looking to try out a 20 tower system in my garden before i go "commercial". Trial & error will be the name of the game & i won't be looking to start growing until march as we're not blessed with your Caribbean weather!

Good luck to ya Tom!
I am trying to commercialise indoor hydroponics to reduce issues with pests. But I am with you on the trial and error. Unfortunately, I'm seeing more errors atm.

Are you in able to share where you sourced your stuff from in China. I wold like to see if it a cheaper avenue for me in the future.