My WVO supply hoses are 3/8" for the supply, 1/4" for the return. Braided vinyl tubing. I have no heating system. Of course I've also not done this over the winter yet. We'll see if heating will be necessary in a few months.

__________________
'84 300CD Turbo 132k (Anthracite Grey) - WVO - My daily driver - Recently named coo-coo-coupe by my daughter.
'84 300D Turbo 240k (Anthracite Grey) - Garage Queen
'83 300D Turbo 220k (Orient Red) - WVO - Wifes daily driver

I'm not a certified mechanic, but I did stay at a HolidayInn Express last night.