I have only just come to realise the lack of the vent, I suppose that the absence of issues like siphoning, slow draining and gurgling diverted attention away. The house is in a rural location with only 3 other buildings feeding in to the sewers in a long stretch. I wonder how the builder got...
I have a bungalow with concrete floors. I'm gutting an existing ensuite and building a new one in the next bedroom; they are either side of a block wall.
The existing ensuite was adapted for a wheelchair user and I have exposed the shower drain to find it looks very much like a toilet waste...