It isn't really necessary. The Emergency pipe does a perfectly reliable job. In a worst case scenario, the primary pipe stops completely...water rises to the emergency level which then takes all the flow. This wouldn't even be anything that needed urgent attention.

In my case, putting 100% of the flow down the emergency standpipe creates an unbelievable noise!

I run with no strainer on the primary. It is just a bulkhead at the bottom of the overflow box. My overflow boxes are covered and nothing larger than 1/4" could get into the box, so I don't think there is any need for a strainer on the primary. Anything that did get in would just fall straight through into the sump.

Gregg's Distributors in the west end carries the strainers pictured above. If your overflow is at least 5'' wide you should be able to fit these. They have a huge amount of surface area, so to plug them up...? I don't even know what in the tank could plug them up. From my experience these work great and pretty cheap too.