My project Hunter 19-2 is moving along. The boat came with no plug in the water ballast tank vent. I tried a 1" drain plug and it slid right in and out even when cocked. I figure it might be a 1-1/8" or 1-1/4" or is it metric? What size and type plug is in your boat's ballast vent hole, a regular boat transom plug, a bait well plug, or ??? Thanks, Jim B