the cap for the drain is available at any rv parts store. Tell them you need a pex cap for the fresh water drain. The valve for grey/black looks like someone has previously been monkeying around under there. That mesh looking stuff isn't stock to the trailer and valves should be accessible outside of the underbelly material. It could be a drain release for a second grey water tank if you have one. Some campers have a separate galley tank, which should show on your tank monitor inside. If so then the other drain valves are located further down from there under the camper
