How to secure a large catch basin where three pipes connect in large catch basin box on a very steep hill so the box won’t move when filled with water in a hard rain?

Basically I have to Tee the water to the sides as it comes rushing down a drainpipe on a steep hill. I want a clean out there too so I want to put a catch basin to Tee the water to the sides. So water will come racing down the hill, into the catch basin, hit the far inside of the arch basin, and then go out the sides. How do I secure the catch basin so when the water comes rushing down the hill at speed, goes into the catch basin to Tee each side, the water won’t push the catch basin eventually down the hill?