Mercury - Drain Plug Gasket FourStroke Series Marine-Grade Seal Material 8M0204692. Overview. Every boater knows there are a few small parts that carry more weight than you'd expect, and a drain plug gasket is one of them. When you're relying on your outboard to get you home across a breezy bay or guide you through a narrow marsh channel, you want to know every seal is doing its job. You want to feel that quiet confidence - that sense that your engine is tight, protected, and ready for whatever