Downgrade Pixel (2016) to Oreo

[v-600]

My pixel has had terrible battery life with Pie (from 4-5 hours screen on, down to 2-3 hours). I was thinking of doing a factory reset but then thought why not just put Oreo back on.

I assume there's not an OTA way to do that?

I've not looked at flashing the pixel before. How easy it it to do?