I have a 2'x2'x2' collection basin at the bottom of my steep driveway. 4 inches up from the bottom of the basin is a 4 inch PVC pipe. That pipe runs under the driveway and deck and runs about 45/50 feet. I'll have to dig a little to find out where it comes out but I know "about" where it comes out. The pipe is completely clogged.

First. I'm going to rent a drain rooter but will one with a 3/8" cable be enough or should I go with 3/4"? Both have the same motor size (1/3hp).
Second any tips on clearing what I think is compacted silt in the pipe?
Third, How do I prevent this from happening again, some sort of screen over the inlet pipe?