New Camper New Problems Septic and Drain issues Please help!

Well i see the valve for the other one is also covered and more to the front of trailer... I did not tear underbelly but i tested it... It is wide open which is fine as this camper is going into the woods as hunt cabin... I will have it hooked up to a septic and will just foam off the opening to keep critters out..... The drain plug i cant figure out ... I have been on numerous sites and cant find the part