I've got an eBay radiator and it doesn't have a proper air bleed valve to fit a clear plastic tubing. There's an opening for bleeding air but it's just a simple screw type plug like the drain cock, so bleeding air is a bit crude but doable, certainly not pleasurable

Is there an air bleed valve attachment I can buy that requires little or no modification or would this involve some custom job to the radiator?
Cheers