Tank Sizing

I have a 9-10gpm demand from my sprinkler system and may have some low flow situations using the garden hose. (The house is on city water). I am going to install a CSV1Z(probably overkill for my system?), and my pump is at 250 ft, 10gpm pump

A while back some of you suggested a 20 gal tank is all I needed.

My well guy insists I need a 44gal tank. He says it will give me 11 gal of draw down? I don't know what that means.

He says he knows what a CSV is.

What size do I REALLY need?

Also, my pump is a 10gpm pump and switch is set at 40-60.

Any advice would be greatly appreciated.

40-44 gallon tank won't hurt anything but, a 20 gallon size that gives you 5 gallons of draw down, or usable gallons, is all you need with the CSV. Some people would even use smaller tanks than that with a CSV but, 20 gallon is the size I have.

Thanks valveman.