There are two mechanisms, but they are not equivalent.
The first mechanism is by changing your umask, but I wouldn’t recommend this, given that you’re aiming for world-writable permissions. See… 
… and…
man umask
The second (and better) method — possibly in conjunction with temporarily changing your umask — is by setting the SGID flag on the directory. This too is explained in the above-linked tutorial.
That all said, the better way to handle the permissions is to, instead of using sshfs for sharing a directory, set up NFS instead. That way you can fine-tune the permissions without having to make the share world-writable.