Go to https://visualmethodexternal.slack.com/admin and invite the new members
Go to https://sameroom.io/create-a-tube and click the slack icon. Authenticate with your slack accoun
Choose the channel on side A from the dropdown list
Then choose the channel on side B from the dropdown list to match the channel in the other slack space and hit create.
This should now connect the channels from visualmethod.slack.com to visualmethodexternal.slack.com