I often just add "whirlpool" which is a fairly reliable Australian forum that started covering telcos but these days will have things about cars, home maintenance, personal health, etc. Or I add "forum" and that can be enough to tilt the results.
I usually add site:reddit.com or site:news.ycombinator.com etc.
Actually google had a way to search discussion gruops, but they removed this feature as forums don't pay for their adds I suppose.