The other is to use the second router as a WAP and switch. (that's on the web.)
I recently moved my printer to a different room in the house. I have a router/modem with a home network that it was connected to. In the upstairs where I moved the printer was moved to there is another router used by a tenant so that there is some separation between out stuff as well as helping with him bogging down the network with all his gaming.
His router is plugged into the Ethernet outlet in the upstairs, so I plugged my printer into one of the spare ports in his router, but wasn't thinking about the issue that it would be two separate networks.
My router has no more free Ethernet ports, so even if I wanted to buy some cabling and crawl through the attic space in hopes I could run a second Ethernet line up there, I don't have an open port. Doing a bit of research it looks like I can connect to the printer, but it seems that would defeat one, if not both of the reasons we have two routers, being privacy/security and bandwidth control.
It seems that the easiest way to solve this is to buy a switch, and go from the Ethernet outlet, to the switch, out to the printer and then his router. I just wanted to get the opinion(s) of someone with a bit more networking knowledge than me.