First you need to join the group. Then add a new search in wave and
enter "
group:gian...@googlegroups.com" without the quotation marks
as the query and whatever as the title. I suggest Giant Bomb. :>
When you search for that, all the waves that have
"
gian...@googlegroups.com" as a participant will show up. Only
members of this group can reply to those waves.
So if you want to make such a wave you just need to add
"
gian...@googlegroups.com" as a participant to your wave. Don't add
it to a wave that has participants that are not members of this group
though because I think that will make the wave go all crazy.