Howdy Paul!
I wanted the hose to be durable yet very flexible. You’re not going to believe this but I wound up buying air hose from Home Depot, Husky 3/8" Hybrid hose. The fittings are simple brass fittings from HD as well. I’m a licensed journeyman plumber so I’m confident the hoses will last a long time. Also it was much cheaper and better then just buying 3/8" hose by the foot, which generally isn’t flexible.
I went with 3/8” to help remove as much pipe restriction as possible so that the system runs as low as pressure needed, without getting carried away such as using 1/2" or larger. The lower the pressure, the lower the stress on everything. The pump is from Amazon, Vivosun, and works great. I also added a small flow meter from Amazon to make sure I always had flow.
The water tank is made from 1/4” plexiglass (.221") because I didn’t want a bucket lying around that I would eventually kick over due to my typical clumsiness. But I do admit that making my own “fish tank” added about $80. I still think it’s worth it.
One last item; everything is opaque in color, even the fish tank is black, because I do not want light hitting the water. Sunlight promotes bacterial growth so I tried to eliminate as much as possible. The liquid is 2 gallons of distilled water with roughly 8 ounces of 50/50 antifreeze. I don’t have feeezing issues but the antifreeze also offers good corrosion protection. NEVER use DI or distilled water by itself. It’s very destruction to anything other then stainless steel.
If there is anything I can do to help you build your system and be blessed, don’t hesitate to ask. 
God bless!