Walking inside the piping, you get to this bit. Leave the water channel and jump down - preferred to the right (not so deep a drop here). Go inside the hole and pick up the goodies.

Get to the top on one of the lifts. Then jump down to the ledge, and pick the goodie up.

After turning the weel and starting the piston, ride it up and push the switch on the next floor. Jump back down, a hole with some serious goodies has opened here.