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The inlet is pretty far up and if it was blocked it would not keep it from operating either. It is double walled and the inlets on bottom and middle all go up to the top anyway.
I have this set up. I think the bottom slits are under my sand bed, but the other two are fine. You have to keep them clean, but I'm running a Mag 36 14' high at full boar so the flow isn't an issue.