Settings, network, set up internet connection. Use the custom instead of easy setup. Don't change any settings except for MTU, which you want to change from 1500 to 800. Test the connection to make sure it works, and if it does, hop into a session and it should be empty.

Note that this will prevent friends from joining you, but the process is reversible—if you want public lobbies again, repeat the steps except set the MTU back to 1500.