gravy train

gravy train (the kind of job that brings in a much higher income than the services rendered would warrant {informal}; any easy and lucrative way of obtaining money; getting paid more money than the job is worth) — легкий заработок; легкие деньги; доходное место; выгодное предприятие; работа не бей лежачего; тепленькое местечко

Example 1: For many years his job was a real gravy train but now the company has become very strict and will not pay overtime.

Example 2: The job was a regular gravy train and I made a lot of money when I was there.

By the beginning of the 20th century gravy was being used to mean money that had been easily acquired, or that was extra in some way, such as a bonus or tip, in the same way that gravy is an extra on top of the basics of a meal. It could also be used for money obtained through extortion or other illicit means.

gravy train was US railroad slang for an easy run where the pay was good. This was adopted into general speech in the 1920s.

See also
[ride the gravy train]