Magnetic levels are great, but only a small subset of pipes are made from a magnetic material; the rest are PVC, ABS, copper, or something else entirely. So what do you use to level, plumb and slope these pipes? You could use Kapro pipe levels.
Made from a flexible extruded polymer, the pipe levels snap onto and stay on standard sized pipes. The pipe levels have both vertical and horizontal bubble vials, and the vials have three painted lines for measuring different slopes.
Available in a five-piece set with levels for 1/2″, 3/4″, 1″, 1-1/4″ to 1-1/2″, and 2″ pipes, you can pick up the set for around $10.