its a low pressure system. The only thing the puke tank would do really though, is keep all that from spraying everywhere. It also lets the cap vent properly, especially if there was air in there. Ive always ran the engines without Thermostats and the cap off the radiator, roughly half full to start with, to help flush the air out of the block and system. I think Dave is probably right, full radiator and a big Air bubble, equaled geyser. Dont feel bad, I've had it happen too