Studies of education and careers in science, technology, engineering, and math (STEM) commonly use a pipeline metaphor to conceptualize forward movement and persistence. However, the "STEM pipeline" carries implicit assumptions regarding length (i.e. that it "starts" and "stops" at specific stages in one's education or career), contents (i.e. that some occupational fields are "in" the pipeline while others are not), and perceived purpose (i.e. that "leakage," or leaving STEM, constitutes failure). Using the National Survey of College Graduates, we empirically measure each of these dimensions. First, we show that a majority of STEM workers report skills training throughout their careers, suggesting no clear demarcation between education and work. Second, we show that using on-the-job expertise requirements (rather than occupational titles) paints a very different portrait of the STEM workforce--and persistence in it (where substantial attrition remains evident, especially among women and African Americans). Third, we show that STEM-educated workers are well-prepared for but dissatisfied with non-STEM jobs, complicating our understanding of leaving. Collectively, these results recommend expanded conceptions of STEM education and careers and contribute to studies of science and engineering workforce transitions and diversity.