Static routes...?

Hi,

We use a pfsense (www.pfsense.com) firewall.

Now say that I have three lan nics (in addition to wan) in this box.
Nic1 at 192.168.10.1, Nic2 at 192.168.15.1 and Nic3 at 192.168.20.1,
both Nic1 and Nic3 with default rules as of wan access (Internet works
ok)..

In addition, any traffic from either Nic1 or Nic3 to subnet
192.168.30.0/24 should be routed via Nic2. Nic2 is connected to another
router with ip 192.168.15.254. (Another port on that other router is
connected to the 192.168.30.0/24 subnet which Ni1 and Nic3 need to
communicate with).

Do I use static routes or nat in this case? Traffic to the
192.168.30.0/24 subnet from workstations connected to Nic1 and Nic3
should be routed via 192.168.20.254 to find the 192.168.30.0/24 net.

pfsense's static routes form contains the following fields:
Interface
destination network
subnet mask
gateway

Thanks a lot if someone can help me put in the right route here

Tor