I was thinking the same thing, but I figured I would make it so this is not possible, so either it would be settled on the bottom or suspended in the water below the grate, which will be very close to the bottom (the grate will only be there just so I can do a dump without having to pull the filter material out). Any water that makes it up thru all the filter material will have to be clear. Because I will be using a slim jim garbage can:
I can pack the filter material in there with a grate on top with something holding it so it keeps the filter material down. In theory it should work just as good and the reason I want to do it this way is because I want to have the water come out higher rather than lower so do a second stepped down falls/stream.
I agree that it would be more ideal to have it go from top to bottom, but im hoping going bottom to top will work as well...
The other option is to do something like you drew up here:
https://www.gardenpondforum.com/attachment.php?attachmentid=961&d=1247513152
and just put an extension on the TEE up a little higher incase the waterline actually has to go abover where you drew it to equalize as the filter gets dirtyer. Im not sure, but now im thinking that would be better maybe. I think Ive got to buy another "egg crate" light fixture cover for my grates thou, which sucks as there $11. Wonder if I could use someting else...maybe I can get some baskets shopping baskets from somewhere.