Rubber Fitting for Small Block Water Pump

I decided to start the car up today and load it with tools as I was planning on driving it from my mom's house to my new house in 2 days. I had the car idling for about 10 minutes and I noticed my engine started to get very noisy (lots of metallic sounds). Well, when I went to the front of the car, water/coolant was squirting off the top of the water pump. Hopefully, I didn't damage/overheat the engine. When I checked my water temperature gauge, after I shut the car down, it read 160F.

I'm glad this didn't happen when I was driving. All of the hoses are about 2-3 years old. I think it may be this rubber plug on the water pump spout. It's cracked to hell. Anyone know of a good replacement? Hopefully not rubber.

Could it be something else? Shouldn't the radiator cap bypassed the pressure to the catch can? Well, I guess if the cap gave out, there would be no pressure.

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