I would remove the hose from the catch can and use the vented cap. Unless your rad is defective at the overflow, you should have solved the collapsing hose problem. If so, then you know that the catch can needs to be vented
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This^^^^^^ try eliminating the catch can and running it with the vented cap! If it still collapses the hose, it's not the can vent!!
And, 20 cars can have the incorrect cap on it, and if no one is running the exact same setup as yours, they are worthless examples! Did any of them have the Jegs bottle you are running???
