Just went thru this with my OMC Cruis-A-Day Jr 4 gallon tank. From everything I read, the diaphragms with the extra hole were for use with the aluminum push button, the rod of which attaches to metal washers on both sides of the diaphragm. Older designs came wing the hole and with later designs, you add your own hole.
As to the filler cap, mine had the chain slot in its washer and the beaded chain.
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