Lots of experience here so I'll bounce this one off of you. Drain in a detached garage with no heat is backing up. First snafu with it in a couple decades. Only thing that drains into it is snow, slush and water from two vehicles that park in it. Manually ran a drain snake down it and think it's frozen up a few feet from where it empties underground into a rock pit. Only open access is on the floor of the garage. NWPA everything frozen over pretty darn good. Would be quite a chore to dig down into the pit. Any ideas how to attack it from above? Thanks in advance.