I put in at Fulling Mill Road. If you follow the road back past the church and down past a few farms, it crosses a railroad track and ends at the creek. I go down here if I just want a nice, afternoon paddle. If the mood strikes you, or you just don't feel like paddling upstream on the way back to your car, you can actually make a day trip of it and paddle all the way down to the Susquehanna, though I think there may be a place or two where you'll have to portage around. Beautiful area with lots of wildlife to observe, the current is mild and the bottom is visible throughout most of the creek.
The only permits I know of is to use the boat launch at the Susquehanna River... PA boat registration is needed, but it's a good idea to have that anyway.
From Hummelstown, follow Fiddler's Elbow Rd. out to the stop sign by the church, turn left and follow Fulling Mill Rd to the end. From 283, exit onto fulling mill road and follow straight to it's end.
Put in at the end of the road is a bit steep, but does level out at the bottom, so once the boat is down there, it's not too tricky to get in. I usually just take-out at the same spot, but you could follow all the way down to the boat ramp at the Susquehanna River if you wanted. There's a concrete ramp, and a floating dock (In the summer) there.