To pull out all the stops is to make every possible effort. They pulled out all the stops, pull out all the stops for it, time to pull out all the stops.
The stops are the knobs on an organ that bring each set of pipes into play, so pulling out all the stops makes the instrument as loud as it can be. The image is exact and the phrase is unusually well documented.
1phrasepull out all the stopsTo make every possible effort.
“For the royal visit, the town will pull out all the stops.”
pull out all the stops is an effort.
From the stops on a pipe organ, which are pulled out to bring each rank of pipes into play.
An allusion to organ stops, which are pulled out to turn on each set of sounds in a pipe organ. When all stops are pulled out, the organ will play all variations of its sounds at once, therefore being as loud as possible.
Etymology from Wiktionary, CC BY-SA
Practised in Idioms