This is the latest design of drain plug that is used on the Watermatic and Watermaster fountains. It pops out to easily clean the many Ritchie troughs which utilize it. By tightening the bolt in the plug, it can be made to expand a little more and fit tighter in the drain hole when necessary. This plug is considered a “wear & tear” part that you can order extra with your unit and keep in reserve until needed. If you are outfitting a Watermatic 100, you will only need one of these plugs. A Watermatic 150, 150s&g, or 300, will require two plugs. Several of the larger feedyard and dairy fountains (Watermasters) utilize it in their design as well. The older versions of these plugs was a black rubber design, then later a white silicone rubber one – Upgrade to this latest new one…The # 18470