Some places require sewer hose supports so hose is NOT laying on ground.
Sewer hose support provides a graduated slope so stuff flows downhill
Course NOT all places/sites need or are set up where sewer hose support can be used.
I carry one and use when appropriate.
IF you really want to have a 'trap' in sewer hose....just spread sewer hose support and let section of hose drop down.
I don't cause a never leave dump valve open (Grey and definitely not Black).
Seen too many sewer flies inside CG sewer connection and don't want them setting up house in my holding tanks.