The lack of an inflator "pull dump" is a recognition by the manufacturers that a properly positioned diver in the water will be horizontal in the water column.(imagine laying on your stomach) So if the diver, vertical in the water column (imagine standing up) were to try and vent air from their wing, very little gas would be dumped. This is why the dump valve in the lower corner of the bladder is the more important feature. The diver, horizontal in the water, will have the gas in the wing at that section of the wing. This attitude will provide for a much more efficient diver in the water.