Methods, systems, and computer-readable medium to perform operations including: determining, based on at least one dimension of an annulus of a wellbore, a respective downhole position at which to position at least one of an upper sensor and a lower sensor of a downhole pumping tool that includes a pump; positioning the downhole pumping tool in the wellbore such that at least one of the upper sensor and the lower sensor are positioned at the respective downhole position; in response to the upper sensor detecting a first fluid level in the annulus, activating the pump so that the pump pumps fluid from the annulus into a tubing of the wellbore, where the tubing carries the fluid to the surface; and in response to the lower sensor detecting a second fluid level in the annulus, deactivating the pump, where the second fluid level is below the first fluid level.