Within Teamwork Chat, you can choose to
        automatically add new users to a
        particular channel by default. 
To make an existing
        conversation/channel into a default
        channel, click the options button (three dots) in the top right of the channel and select Edit channel.

In a conversation, you will need to convert
    it to a channel first by clicking Convert
        to channel. 

In the create/edit modal, select the Automatically add new users to this
        channel option.

Once selected, every new member will be added
    to this channel as default. 
Note: Only a public channel
    can be set as a default channel. 
