When configuring a static route, you need the destination network, its mask, and the host IP of the interface that the traffic needs to go out.
So, if you have a multihomed server with 2 IPs: 10.10.10.100 and 172.16.10.100, and you want traffic to go to 192.168.10.100 (assuming that the router on the 172.16.10.0 network knows how to get to the 192.168.10.0 network), you use the following route statement:
route add 192.168.10.100 MASK 255.255.255.0 172.16.10.100 -p
