Accessing pc's on other network.

Simply - I have 2 networks running behind the firewall.

I need to access a 10.10.10. network PC from a 192.168.1. PC

I have given consideration to adding another Nic and bridging. 
But I also found a post suggesting setting up a packet rule to do this. Obviously this would be easier if possible.

Any info gladly received.

Thankyou

This thread was automatically locked due to age.