On Wed, 18 Apr 2018 13:15:16 -0700 (PDT)
Mr Fuxit wrote:

The easiest way to soak emulsion is to coat it with a stiffish mix of
wallpaper paste. It scrapes off pretty easily after an hour or so.

As I discovered to my cost when several coats of emulsion failed to
cover some marks on a ceiling, and I decided to paper it instead ...