class MemberManager(models.Manager):

    def get_queryset(self):
        return MemberQuerySet(self.model, using=self._db)

def in_group(self, group):
    return self.get_queryset().in_group(group)

def not_in_group(self, group):
    return self.get_queryset().not_in_group(group)


class Member(models.Model):
    objects = MemberManager()
Django: Give custom filtering methods to `QuerySet` objects of a specific model