Square Head Brass Plug on PCM 343?

[headfirst]

Does the square headed brass plug on the right look familiar to anyone? I think the plug on the bottom is the water pump j pipe drain plug, but I can't figure out where the square head plug on the top came from. I found it in the box where I keep my winterization supplies (extra impeller, boat tools, etc.) for our 09 RZ2 with PCM EX343. I'm trying to make sure everything is in place before it goes back on the water this year. What drain am I forgetting, or do I have an extra plug?
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[Bravo Golf]

Is the size 1/2" ?

Could be the bilge drain plug.

[talltigeguy]

Or I have seen plugs in the engine that look like that for the heater. You remove the plug, then put a hose fitting on it to go to the heater.

It does look just like an extra hull drain plug.

[IDBoating]

The square drive one looks like the plugs on the V-drive for changing its fluid. I do all of my own winterization and minor service and that's the only place I've seen a square-drive plug like that.

The hex head plug(s) look like the drain plugs on the exhaust system. I have the CATS exhaust and there are two different sizes of drain plugs. Oh, just remembered, there's also one that looks like that on the bottom of the water circulation pump (not the raw water pump).

[BCRider]

^correct

first picture #4 location. Looking at the back of the boat from the cabin down on the left side. Will need to remove the wall

Second Vdrvie for square top

[JohnnieMo]

Interesting BC Rider. The 2013 PCM manual says nothing about that plug. They instead ask you to disconnect the 2" hose coming from the transmission and drain there instead.

[IDBoating]

Now that there's an illustration with reference numbers: The hex head plugs in the photos look like the exhaust drain plugs at locations 3 and 5 (two different sizes), and the circulation pump drain plug at location 2.

I do not know what kind of drain plug is in the transmission intercooler (location 4 in the illustration) because in addition to PCM's explicit recommendation to disconnect the hose, disconnecting the hose is almost infinitely easier than accessing the drain plug. At least on my EX343, the intercooler is mounted such that its drain plug is basically impossible to reach. Besides that, removing the hose has two other advantages: 1) It far better drains the cooling system in that area, and 2) it allows you to suck out any remaining water by holding a shopvac hose to A) the end of the hose and B) the intercooler. (A) works best if you've already removed the 1/2in drive drain plug in the v-drive, and (B) works best if you've already removed the raw water impeller, since in both cases this opens the water circuits to ambient and thus the shopvac can really dry out those portions of the system.

EDIT: By the way, my engine cooling system is not plumbed the way the illustration shows. My raw water path, starting with the lake, is: throughhull, raw water strainer, v-drive, intercooler, and finally raw water impeller pump. Obviously everything prior to the raw water impeller pump is operating under suction instead of pressure.