One barrier to breast cancer diagnosis in low-resource settings is that devices for core needle biopsy (CNB) are either disposable and expensive, or reusable and susceptible to internal contamination. Through interviews with field workers and verification experiments, we identified that a common, commercially available, reusable CNB device allows contaminants to enter the driver chamber during firing, necessitating laborious cleaning of the entire device after every use. We introduce a novel CNB device attachment that eliminates this contamination mode and interfaces with existing commercial reusable drivers and low-cost disposable needles. This attachment repositions the driver–needle connection to the exterior of the driver, preventing retrograde flow of blood. Using an unmodified commercial CNB, we replicate chamber contamination by firing into a body fluid-mimicking glycerol solution. Prototypes were tested for their performance in eliminating this contamination. We tested the effectiveness of a cleaning procedure to reduce trace contamination by using a fluorescent dye and measuring the intensity of fluorescence after cleaning. The device's ability to reliably and consistently biopsy tissue with the novel attachment was evaluated using breast tissue models. In these tests, a reusable CNB with our attachment exhibited no measurable internal contamination, and maintained full biopsy functionality as measured by tissue sample weight and length. Minimizing internal device contamination would simplify the cleaning process for reusable biopsy devices. This would improve the accessibility of breast cancer biopsies in low- and middle-income countries (LMICs).