There's a bottom section that snaps onto the MJ1200 intake that is a slotted strainer to prevent larger items from getting sucked in. The strainer is packed in plastic bag with the other accessories.
60 pounds of LR
in a 100 gallon is not a lot of rock. For biological filtration you should be using 1 - 2 pounds of rock per gallon of tank capacity. I have about 185 pounds of LR
in my 125, plus another 15 pounds or so of LR
rubble. My rock is all pacific rock so it is very porous. I have more than I need, but if it was Caribbean rock it would be about the right amount.