Natural Carbonation in 2L Soda Bottles - A little help

Greetings,

I'm getting back into brewing now that I've stopped traveling as much, and I'd like to explore an alternative route to bottling. One thing I distinctly remember hating is the washing of bottles. It's the probably the biggest single reason I got out of brewing other than frequent travels. Since then, it's come to light that one can bottle in plastic soda bottles.

After searching through the forum, I've discovered that yes, it is possible and reliably so. I understand the pitfalls of the clear bottles as well as potential leaking. I know that 2L is a lot of beer at once, which is why I will be splitting the batch between 2L and 1L bottles.

There are a couple things I have been unable to find.

1. How much head space do you leave in a 2L bottle when naturally carbonating the beer?

1a. Do you squeeze the bottle until the beer is just at the top and then cap it? Or is the remaining oxygen in the head space irrelevant?

2. The bottle I bought are Soda water, with nothing other than, well, soda water. So... is there any reason I can't just use the water from the bottles to make my beer?
2a. Should I break the seal and let them go flat first? I'll be doing a partial boil, so do I just open and pour for the boil, and flatten the rest?

Thanks so miuch.

Mark

Sometimes I fill up a seltzer bottle or two from a batch. It's nice to be able to see/feel when it's carbonated without having to refrigerate and try a bottle.

I've filled them almost all the way full, squeezed out the remaining air, and screwed the cap on really damn tight. You'll know it's carbed when the headspace is back and the bottles feel firm.

If the seltzer tastes fine you should be able to brew with it I guess, the CO2 will come out as it heats up. Maybe pour a glass of the seltzer, let it go flat, then try drinking it to make sure it tastes OK to you.