squid. How to send packets to a specific interface?

Question

Squid

Good day. I have a laptop running Windows XP.
1) It is connected to wi-fi, ip address is 192.168.1.102.
2) A USB modem with ip address 192.168.8.100 is inserted into the laptop.
I need to set up a proxy server in order to connect via local network via port 8051 and access the Internet via a USB modem.
Previously, I used 3proxy, in the settings there was this line: proxy -n -a p8051 -i192.168.1.102 -e192.168.8.100 , that is, all packets were sent via the USB modem. How can I do the same using Squid?
I apologize in advance for possible inaccuracies in the wording, I hope the question is clear.

Answer 1

Here is a similar Squid question and a few external IPs

Answer 2

In the squid config, the tcp_outgoing_address parameter.