Adding coolant?

[Overspendin']

I'm almost embarassed to ask this, but how do I add coolant to my FWC Atomic 4?
My boat is a very early Catalina 30, yesterday I changed out my pump impeller and lost a fair bit of coolant to the bilge.
There is what looks like a coolant tank way up under the galley sink, but I can't see an easy way to access it...suggestions?

[Don Moyer]

If you follow the hose from the back of your manifold, it should lead to the exchanger, just below the fill cap.

Don

[Overspendin']

Thanks Don,
I figured it out...DUH.
The heat exchanger was pretty much obscured by a water filtation system the PO had installed.