blocking ports

How can I set the firewall for one VM to block all outbound traffic except for a few ports? Im trying to give someone a VPS but I want to keep it from seeing my local network. I would prefer to do this using the website, but I can use the command line for the server if needed

Hello, I using a 3 Node Proxmox 4.1 Cluster with PVE-Firewall. The BSI Team makes a Pentest on my Server and have reported, that rpcbind and squid-http port is open. So i think ok, and add rules to drop the ports 111 and 3128 tcp/udp. But the Firewall doesn't block the Ports (other Settings...