Bongo Fury

Evening all, does anyone have any idea about the coolant flow direction to the rear heater? I can see the two pipes under the drivers side sill. I also need to ask the internal diameter of the pipes?? Many thanks Duane.

This diagram from Steve Widdowson's coolant threads might help, RED are the hot side and BLUE the cool returns;

Thanks. I'm guessing the pipes are 18mm internal diameter??