/diy/ - Do It Yourself

I'm building a hydraulic ram pump, pretty much have it done. It uses a 1 and 1/4 inch drive pipe and a 3/4 inch delivery pipe. I plan to use irrigation tubing for the delivery. Thing is 500 feet of 3/4 inch delivery tube costs $200 but 500 feet of 3/8 inch costs $40.

Is there any reason i can't use smaller tubing?