Using iptables instead of redirect-gateway in config file

[terence]

I have setup a client and server successfully using the simplest how-to here. I redirect all client traffic to the vpn using the redirect-gateway directive in the config file.

Both client and server are Linux Ubuntu machines. (EC2 server). How can I use iptables on the client instead of redirect-gateway?

I have spent days searching for examples. Surprisingly there's very little on that, and nothing works.

It comparison, it's simple to use iptables to redirect all the tcp and DNS traffic to TOR. The example there works.

I don't know this is needed,
sudo echo 1 > proc/sys/net/ipv4/ip_forward
because it got fsync errors. I remembered doing something like that on the server without problems.

The reason for using iptables is that I found out how to, for example, direct some users and not others to the vpn.