Hey guys

The previous owner of my bike seems to have bought his tools from somewhere that has a different standard for mm Nearly every bolt i've had to take out has been almost round. I want to change my coolant but the cylinder drain bolt is as round as they come and I was wondering if anyone can think of a way of emptying or flushing the old coolant out without removing the top bolt?

I've thought about removing the bottom drain bolt and running water through it or running the engine for a few seconds but not sure - any ideas ?

Thanks