How to configure iptables to properly forward to a Dansguardian port?

Question

iptables

Debian 7 has mitmproxy installed as http(s) proxy.
In rc.local:
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 8080
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 443 -j REDIRECT --to-port 8080
How can I get traffic from the proxy and send it to Dansguardian on port 3129?

Answer 1

mitmproxy.org/doc/features/forwardproxy.html ?