I am wondering if any other units have the same issue our unit is having. We use a closed system for our UAC's, and when drawing gases, we have been getting diluted samples, despite drawing back to the syringe. We are now having to draw off an additional "waste" just to get an accurate sample. Just wondering what other units have encountered, and how they have over come them. Also, if anyone "loves" the system they are using, if you could include that in your reply, that would be great....always looking for new products that work great =) Thanks for your time!