@GoodTruble
I'm not sure about that gasket, the guten is welded at that point. I do know that you can swap the metal up tube for a sightglass, might be some info on the kegland site about that and it may show if there is a gasket there.
Having looked at your pictures which were posted but my page hadn't updated that's a lot of grain.
I've noticed when you turn the pump off the liquid siphons back, if your pipe was sitting in the grain bed and it was turned off it would siphon grain back and that might account for this amount of grain. But grain going down overflow, or through the handle holes or perhaps just missing the malt pipe and going over the sides when doughing in could be the cause as well.
The only time my pump blocked was when I turned it on during the boil and then really hot wort / boiling wort was in it and it blocked. I just turned off the pump lifted the tube out of the wort to let it siphon back down, this seemed to make a good flush and if that didn't work just fired a turkey baster load of wort back up the tube.