Any idea what this cold water tube is for?

[sundown858]

These two tubes are coming from under the bathroom sink cabinet. One side of these tubes go to the faucet and rest of the trailer. The other side (pictured here) go through the floor to the underside of the travel trailer. When I connect to city water , the blue tube gushes and I have no water in the faucets. Is that blue tube supposed to be capped like the red one so pressures goes throughout trailer? If so, any idea how to cap it. It's kind of tucked way back there.

 

[Scotttkd2]

The location you describe could be a low point drain, but it should have a valve to turn on and off. Is there a valve up in the cabinet maybe??

 

[DennisT]

On our last coach we had those same type.

The hot / red was capped with no actual valve to drain.

The blue /cold had a valve where our water pump was to drain that side.

Should be a valve upstream of the blue line to close that drain.