What good are low point drains?

maillemaker wrote:

The answer would be, IF you can get to the area above the floor where the drains come down, do a little plumbing work and put valves above the floor and run pex down for the drains.

In my RV, the valves are inside the house (2 under the bed, two under the bathroom sink), and they have drain extensions that go through the floor to exit the RV.

Same with our 1990 trailer. - the valves are inside and only lengths of open pipe go to the outside. And the low point drains are how I winterize. Let the water out - also clears out the water heater and then blow the lines out with air.