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That banjo fitting probably has (about) a two foot piece of small hose clamped to it. That short hose was led up to a tie off point beside the engine on our '88 boat. The prior owner had thoughtfully put a cork in the top of the hose to keep bugs out.
My system looks like yours... Nice picture. The issue is that the end of that hose has a fitting capped by a 1/8 NPT plug. If you remove the plug, you will see that the hole is very small, and you cannot put pump-out hose in there, so you have to connect the pump directly to the fitting. Others have suggested a hose barb to connect to the hose on the pump. My vacuum pump has a hard plastic 3/8 inch hose, and I will be getting a "quick-connect" adapter to attach it. I am learning along with you, but I think this should work.So I have this tube to aid in oil changes but I dont know how to access where I assume there is a ball valve on the bottom. This is my first inboard so I am learning by doing with your help.
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In case you find no luck with that anode, a few of us here have replaced our original water heaters with new from Isotherm. My original had a rusty outer casing and the water was foul smelling. Replaced with Isotherm with stainless steel tank, rigid foam insulation and hard plastic outer shell. Temperature-regulating outlet valve and combination pressure relief/drain valve included.
With the supplied hoses, the one with the wire inside was the right size for the tube. I ran the motor for five minutes and still had to let the tube sit in there after gurgling to let more oil in the tube. Maybe didn't get hot enough to move quickly or the banjo valve is slow
What engine do you have in your boat?
The M40 Universal 5432
Be careful not to confuse the "fresh water" in the engine cooling circuit (which usually is mixed with coolant), versus the "house water" system which serves your head and galley sinks. The engine is fitted with a heat exchanger which uses raw sea water to cool the engine "fresh water" coolant circuit. The water heater usually has an internal coil which uses the engine coolant "fresh water" to heat the "house water". Check your hot water heater to see that it has four plumbing connections: house water in, house water out, engine coolant water in, engine coolant water out.
Thanks for assembling this answer. This is helping me understand some of the pictures I took before I our recently purchased 38 to bed for the winter. (It doesn't help that some of the photos are oriented "upside-down" and close-up.)
Sorry if I didn't read far enough back, but I'm unclear what you're trying to accomplish. The anode change? And do you mean pink coolant or winter antifreeze or something else?
I was unable to get the anode removed or be confident that all the clear water was cycled through the water heater so I added a bunch of the pink anti-freeze (Suitable for potable water plumbing)