I owe your plumber big time! I put in a vent and now my darkroom sink drains every time.
You and Michael have hit the nail on the head. A scene that meters 9 stops difference between important shadow and important highlight might need to be treated in the darkroom like it has 10 or 11 stops.
Awesome for you, glad to hear your plumbing is working good.
"The difference between a very good print and a fine print is quite subtle and difficult , if not impossible, to describe in words."
---AA (The Print)