The Solinst Model 429 Stainless Steel Point Source Bailer has dual ball valves, top and bottom. This prevents a sample collected at a discrete depth from mixing with water from other depths during retrieval. It is a simple and cost-effective device for aquifer profiling, and collecting samples from distinct levels. Purging and disposal of purge water can be avoided. The miniature 0.5" (12.7 mm) diameter model is ideal for use in narrow tubes and direct push devices.