The standpipe actually 1.5" PVC and is OK so I plan to reinstall it. The standpipe is centered through the middle of both the cup and basket.

You are correct - in normal filtered operation, the filtered water is forced through the sand and returns via the standpipe; unfiltered water is routed through the MPV, discharged into the overdrain cup, and then through the overdrain basket. I imagine this is to disperse the water 360 degrees, and reduce the velocity of the water stream which would continuously stir up the sand.

Perhaps I wasn't clear in my original message - I would reinstall the standpipe, which would allow filtered water operation to continue. But given that the basket isn't available, and without it the cup is useless, I am considering not installing these two items. Also, as said previously, the Praher MPV appears to have a dispersing design that the original MVP didn't have. So, if I'm right about the purpose of the overdrain cup and basket, I should not need them.

But, if the purpose of the cup/basket is water dispersal, why not call them that rather than overdrain???