help needed digging hole

I could use some help digging a hole in my garden to drain water from my downspout. Hole should be about 1.5 to 2 feet wide and about 4 - 5 feet deep. It’s clay soil so not easy to dig through. Will then fill the hole with 2 - 3 feet of gravel, change some piping which I will have purchased, and fill the rest of the hole. I had this done to another downspout about 2 years ago and it worked great. Unfortunately I am an “experienced” human (meaning up there in years) with a bad back and unable to dig the hole myself. It took about an hour to do this last time so plan on 1 to 2 hours. I will supply a shovel and materials. Any recommendations? thanks Jamie