Stowaway is a collaborative CoinJoin transaction between you and the person you are sending to. It doesn't appear as a CoinJoin on the blockchain and the true amount sent is not revealed on the blockchain. This makes a Stowaway one of the best tools you can use in the bitcoin privacy arsenal.
More information on Stowaway can be found at https://docs.samourai.io/en/wallet/privacy-enhanced-transactions#stowaway