I have set up a printer on a separate subnet for security reasons.
The printer is on lan4 with IP of 192.168.10.2 with DCHP and a default gateway at 192.168.10.1
My PC in main lan1 is on 192.168.1.10 Lan1 with DCHP and a default gateway at 192.168.1.1

I have interlan ticked for Lan1/Lan4 check box.

I can ping the printer OK. However, I cant add it as a printer as it is not discoverable. Is this something to do with the printer broadcasts not getting broadcast between subnets? Is there something else I should setup?

Have you tried hardsetting the IP address on the clients rather than letting it be discovered ?

admin's advice is good here.
Broadcast won't work between networks (so 192.168.1.0/24 can't "discover" anything on 192.168.10.0/24), each network is a self-contained broadcast domain.
Depending on your OS, a hosts file might be of assistance ?
Cheers
Simon

Thank you I will try this.