I filled it with 150psi of nitrogen. I stopped by my old work, they build pressure switchs, so they have large high pressure nitrogen tanks I used to fill it.
I did use alcohol to clean it. Perhaps there are better options, but after I had it thoroughly flushed I used a vacuum pump to evaporate out any remaining alcohol.
The dampening was good. It's now about 12K miles later. 10k of that was riding cross country and back. The bike is drastically different than it's stock form, but I can not really say if the 10 weight oil was better or worse than 5wt.