Saw an interesting device in the home store today. Replaces the need for a
vent on a drain line. Essentially a 6" nozzle with a one-way valve to let
air in but not out. Probably been around for a while, but first time I've
seen one.

Has anyone tried one of these? I daren't ask whether it meets code.....
Presumably would only be workable in an accessible situation such as a sink
or basin.