I just figured out a technicality that can save others time to turn a wired printer (with tcp port) into a wireless printer.
My printer is hooked via ethernet cable to dd-wrt router (my setup is 2 routers: one to dsl provider, and another DD-WRT for in-home users). My laptop is linux Mint 19 / xfce4, but also tried from windows 7, the printer couldn't be found on either network.
Of course this has been done before, BUT in my setup, the printer could not be seen on either router. This was solved (after several trials) by:
print the configs page of the printer, showing its ip address 192.168.0.101 (but both my routers were at different sub-nets: 192.168.25.xxx and 192.168.75.xxx) and i had no way of making the change inside the printer to assign it a different ip address (than 192.168.0.101).
modified my dd-wrt own address to match the printer's expected subnet by the printer (192.168.0.1) -- now the printer became visible. (you can figure the rest...) now I could open its configs screen via browser, and from there i modified its ip address! phewww.
now i could assign it the ip address I want, to match my usual subnet (192.168.25.111) and it was visible.... The rest is just setup from the xfce printer admin screen, add the printer, print test page wirelessly successfully, etc etc.
I hope this saves the next person "not seeing" their printer in router admin page...