Rear Heater Line Question

[XAlent]

I've done a search but couldn't find the answer I'm looking for. Does anyone know which of the rear heater lines is the feed line to the rear heater, i.e. the one supplying the hot water. They run parallel to the chassis, I want to tap into the feed line where the two rubber hose joiners are. Is it the one closest to the sill panel, or the one closest to the transmission?
Cheers

 

[Rover4]

Alright, I'm curious...why do you ask?

I wondered the same thing when I flushed my cooling system when switching over to Evans Coolant. I couldn't figure it out so I flushed, and reverse flushed, through both sides, twice.

 

[XAlent]

I'm installing a heat exchanger for on board hot water / shower. The unit I have fits there nicely, saves cluttering up the engine bay more. I'll have to trace them back to the engine, but they disappear for a little bit and it's difficult to keep track of which one is which.