Some have a float/plunger that rises up with level increase and blocks the vent.
No venting..no more fluids can get in....close dump valve, press down on float/plunger to vent and allow drain line to evacuate into tote.
Then make several trips back & forth to dump station to empty tote.
We have one..........used it once.
After that I just move rig to dump station dump and then reset 5vr back up.
For me..less hassle and I'm not dragging a tote full of stuff down the campground road hoping the handle doesn't break, a wheel doesn't break, tote doesn't tip over, tote doesn't crack/develop a leak while in transit and I don't have to make several trips..........let alone mess with dumping the tote.
Just me........but I can move 5vr dump and be back in site just as quick as I can do one round trip with tote