Quick answer: To clear the Garfield: Escape from Monday Nurmal boat syrup level, jump on a large button and call Garfield's helper. The helper uses a super straw to drink the syrup, lowering the level so you can continue toward Nurmal's boat. Repeat at each button you reach. Source
Players also call it Nurmal boat buttons or Nurmal syrup level.
How to lower the syrup level
Jump on a large button
Find one of the large buttons and jump on it. Source
Call for help
After landing on the button, call Garfield's helper. The helper drinks syrup with a super straw, lowering the level. Do this at each button you reach. Source

If the syrup level has not dropped, make sure you call the helper after jumping on the button; the helper's super straw is what drinks the syrup. Source
FAQ
Jump on a large button and call Garfield's helper. The helper drinks the syrup to lower its level. Source
Jump on each large button you reach and call for help there. Garfield's helper uses a super straw to drink the syrup. Source
Jump on the large buttons and call Garfield's helper at each one to lower the syrup level. Source
Related
- How to Escape Nurmal's Prison covers the separate prison escape puzzle.
- How to Get Past the Jelly Crocodile covers another obstacle in the Sugar Seas.
- How to Power Squeak's Barn Portal covers the separate portal objective.