Lad in work always uses hot water to fill the ketle and fills it through the spout. I've never seen anyone else ever fill a kettle with hot water, something I would never do, I'm sure it's grand, but it turns me off making a cup of tea/coffee from the same boil.
Also, why do people fill through the spout? There is a little button at the top of the kettle which pops the lid, fill her up and press the lid down, how hard is that, and you won't spill water all over the outside of the kettle. There is a filter in the spout, so when you pour it catches any little bits of debris that may have come through the water system. So to fill through the spout, you could have the bits of debris on the wrong side of the spout and they end up right in your morning cuppa!
So how do you do it?