That plug has a very aggressive pitched internal tip that is supposed to hold it down in the pipe, and the plug being an O ring style plug only has to be held in place. I used tie wraps all around mine, have a new pipe in the garage for 4 years now, still have not felt the need to drain the cooling system to change that large assembly. As long as that plug stays put, it will hold system pressure. It pops out because the tip of the plug inside the cooling system breaks off, extremely easily, so Joe is spot on. There was one available on Rockauto.com which I bought. It is aftermarket, but I have it in my garage still in the box and it appears to be anatomically correct. If you can still get that hose from Motorcraft, it would be a lot more $$ than the rockauto one, which I think I paid $35 for. My first time around, which included replacing the plug that failed as yours has, with all OEM, came in a kit with all of the hoses and a new thermostat and housing. Maybe 5 hoses came with it. All hoses came with new spring clamps. Some of those are extremely stout and if you were to go into this job, you would definitely need the remote cable driven spring clamp tool to change these hoses, as some of them are in very poor positions that no pliers would be able to open and release from. Luckily for us V6ers, there is only a tiny amount of plastic involved in our cooling systems. The hose that contains this plug lasted less than 5 years after changing it before the plug tip disintegrated again. It's been held in by tie wraps since that happened. And haha, I have had to use the port and changed the tie wraps each time.
