Water Heater Puzzle

I'm in process of replacing my water heater (gas). I've got the new one out of the carton and it's got all the normal stuff plus something extra: a bag containing two 3/4" galvanized steel nipples. Each is 2" long with a blue plastic lining running the length of the inside and protruding about 1/16" at each end. If I screwed one down on the dip tube (which seems to be the same color plastic) effectively the water wouldn't touch the galvanized nipple. I don't know why I'd want this on the hot side though.
But wait, there's more. At one end of each nipple attached to the blue plastic lining is a (also) blue plastic ring bringing the outlet diameter down to 3/8". Inside the ring is a black rubber flap, very thin, and attached only on one side. Except that it's rubber and there's a small gap around the black rubber and I can blow the flap out of the way in either direction, it could be a check valve. There's no directional arrows on the nipple.
The only reference in the manual is on the repair parts schematic where these nipples are described as: "Nipple w/Heat Traps". In the installation section the diagram shows an arrow pointing to the hot and cold inlets with the description: "3/4" Threaded Nipple". Nothing about heat traps. The impression is that you could use any 3/4" nipple.
Does anyone have any idea of the function of these special nipples and which way they go in. I'm a little worried that the rubber flap is so flimsy that it'll break off and end up blocking some faucet. Maybe it's a partially disconnected washer (the hole hasn't been properly punched out) but why would they reduce the size to 3/8"?
If no one has any good ideas, screw them. I'll just put back the 3/4" brass nipples I removed from the old heater.
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Galvanized pipes rust from the inside out. Good to have both nipples plastic lined - they last much longer.

The black rubber thing is a heat trap. Keeps the heat inside the heater when the thing is not being used. A good idea, but this implementation needs work if you ask me. See below for a better way.

You can use any 3/4" nipple as long as it's plastic-lined. You just don't have the heat trapping capabilities with a normal nipple.

No, the rubber flap is the heat trap mechanism. I don't think it matters which way they go in, if it did the mfgr would likely have arrows painted on them to indicate the direction of flow. However, I think the things are likely to be completely ineffective in a few years after the rubber flappers get permanently bent in the outflow (hot-side) or inflow (cold-side) directions, or they break off. Plus, they don't truly stop all the heat from getting out.
A better solution is to make a heat trap out of copper pipe. This kind of trap is nothing more than a loop. Heat rises, but it doesn't sink, so the heated water will stay in the tank when hot water is not being used and it won't radiate heat out the first 10 feet or so of pipe coming out of the tank.
I have such a trap on my tank and the outlet side of the heat trap is as cold as the incoming cold water pipe if the tank has been sitting for a while. My loop was 1/2" copper pipe rising 12" out of the heater's hot side, then across 2", then back down 12" and out to the house. The length of the up & down sides of the trap do matter, longer is better up to a point. 6" probably isn't long enough to truly keep the heat in. (If necessary, the same kind of trap can be applied on the cold water side, but it probably isn't necessary; the dip tube does the trick there.)
Because this involves laws of physics, it will always work and it will never have a piece break off and plug up something. Supposedly you can take a long length of that so-called "flexible" copper pipe and make a loop out of it - it would do the same thing - but have you ever tried to bend that stuff?
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I would go ahead and use them. I agree it sounds questionable as to how effective they will be long term, as they may tend to stay open after years of use. On the other hand, there are many great synthetic materials today that have properties well suited to particular applications. If the manufacturer chose the right material, they may in fact work very well.
And while these aren't perfect in stopping all the heat, neither is a heat trap constructed of pipe. You now have a loop of several feet of pipe that you have to insulate, and that will still lose heat, plus some heat does transfer through the water anyway, etc.
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