Tell me about this puke can

And that is the other problem with this design. That cap is air-tight and even has an O-ring? Without some kind of vent hole, this unit will only allow a small amount of coolant in, before the pressure with the radiator becomes equal...at least I would think.

Here is mine. This is a stainless tank from Summit. It came with two pipes sticking out the bottom. One connects to the radiator and one is the overflow. The overflow pipe runs up high inside the can. This line is the vent. I assume the one in the original post is this way as well. The cap is sealed but the tank vents through the pipe in the bottom.
Summit Racing SUM-300103 Summit Racing™ Stainless Steel Overflow Tanks | Summit Racing

I didn't want to run a rubber hose from the tank to the radiator so I modified things a bit. I cut off the center pipe in the bottom of the tank and drilled it out for a 6AN bulkhead fitting. That allowed me to make and attach an aluminum hard line to the overflow tank and run that to the rad. Now I only need a small section of rubber hose.
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