mt300nv2 print server

Trying to use mt300nv2 as print server but need help.
Idea is to connect printer to usb of mt300nv2, then wirelessly connect mt300nv2 with my main router and thus making printer available on home network.
As i read that would be possible with p910nd daemon?
I successfully updated apps on mt300nv2 OpenWRT and installed apps needed for p910nd, set it up, but can’t figure out how to connect mt300nv2 to my main router for printserver functionality.
Tried WDS connection but it’s not working right. After i reset main router mt300nv2 wont reconnect automatically to main router.
Also need help to set up firewall (need to forward port 9100 to main router).
Any help appreciated.