ooooops - sorry to hear that about your AVR.
I have the Ryobi 6900K model and also didn't change the oil initially; it was pitch black when I finally did manage to change it. Yes, the bolt at the bottom is for draining the old oil out - I lifted my generator on bricks a bit (as I didn't have a pan, but a jar which was high, and tilted it slightly, to make sure all the old oil is out).
I also managed to get the manual from Ryobi via e-mail, as I couldn't find it on their web site. I attach it here if anyone can use it - it is at 5.97 MB file on MEGA
I used the Castrol oil 5W30 from Makro; this specific generator needs 1.1 liters of such oil (the Ryobi guy said over the phone it can be "SAE30 or SAE40").
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Safepowering!
A question though - what do you do with the old oil? Is there some place where you can drop it off?