Originally Posted by Eddie Longest
I'm with Bob keep the greywater valve closed until you dump. If left open your trailer becomes a vent for the CG sewer system and with a Scamp
the greywater vent is under the trailer.
Not likely, but I did not recommend leaving it open... My point was that you could harm the trailer by leaving the black water valve open, not so with the gray.
We use a garden hose to drain graywater when we have on site sewer, no problem yet. The hose provides a natural trap anyway. If you use the 4" hose as you say there is no harm in keeping it hooked up and closed then draining it each day with no adverse consequence. With only 18 gallon capacity it is a luxury to be able to keep the gray water empty between showers.
Campground sewers are vented at all substations.