VPN Client on Synology - how to route all traffic through it?

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I've had a VPN client running on my NAS for a while expecting the traffic to go through it, rather than the LAN (wrong, it seems)..

So my question is this, apart from setting up (and connecting) the VPN connection as a network interface, what do I need to do to route all traffic on the NAS through VPN?
(I tried changing the "Default Gateway" to be VPN rather than LAN, but then I had no inbound traffic..?)

 

[Scope]

Thank you very much @visibleman , that seems to have done the trick.. I will look at using a docker, as it does slow down the speed quite considerably.