@ the poster above me:
You found the free jiggy (jiggy tamper) under LOG's factory? If you have, then you're in the right place, but in order to get the stop n swop crate, you have to have gotten the green stop n swop egg in Banjo Kazooie arcade. If you haven't done that, then you wont be able to get the crate
@ the OP: In order to get through the grate, you have to have beaten Grunty in act 4 of the Jiggoseum. After you do that, you can get the scuba seat on your trolley so you can unlock the three underwater grates in showdown town. If you don't have the scuba seat, the gates wont open
...HERE AT THE END OF ALL THINGS...