I believe the 'plugs' you are referring to on the red and blue water lines are actually the 'low point drains' to drain all the water out of the lines.
The plugs, when installed properly, should show zero leakage. I'm thinking someone may have cross threaded the plugs and ruined the threads so they will not seal and hold water under pressure.
The 'fix' would be to replace the plugs and the connection they fit into on the hoses.
Just my thoughts without seeing photos.
2012 Fun Finder XT 276 Toy Hauler & Harley Davidson Ultra Classic with Condor wheel chock
2014 Dodge Ram 2500 AT 4X4 Crew Cab 6.4 L Hemi, 373 gears, tow package, Rambox option, Revolver X2 tonneau cover, Equal-I-zer anti-sway hitch.