Many months ago I followed a discussion about this funnel and when Bird indicated that he was using one I thought "Hey, that's good enough for me" and I bought one. As a test I poured a little water into some diesel fuel and the funnel seemed to separate the water as advertised. I've been using the funnel ever since. I don't keep a great deal of diesel fuel on hand and I buy from a reputable dealer who has a fast turn-over so I haven't gotten any bad fuel to my knowledge, however, I always use the funnel "just in case" I regard it as cheap insurance (suspenders and a belt).