The round Crusader gaskets have tabs that stick up above the parts for easy identification. The "one hole" gasket has 2 tabs and is always used at the elbow. The "three hole" gasket has only 1 tab and is always used at the bottom of the risers to allow maximum water flow to fill the manifold and riser.
Note: When using the stainless blocking plate use 2 gaskets and sandwich the stainless plate between them. Since the plate blocks the flow of water either gasket can be used.