Where a drain here keeps blocking, the pipe is usually coated or silted rather than obstructed at one point — and that is what jetting addresses.
Sand and scale together
Island drains collect sand from showers and, in older cast iron, decades of internal build-up on top of it. A cable passes through both and leaves them in place. Jetting takes the line back to the pipe wall.
After roots have been cut
Once roots are removed from an old lateral, jetting clears the fine material left behind that would otherwise catch the next thing to come down.
Outdoor shower lines
These carry more sand than anything else on the property. If yours has never been cleared properly, that is usually where to start.
When we will say no
This matters more on Sullivan’s Island than most places. Very old cast iron or clay that has already lost wall thickness may not survive the pressure, and jetting it could turn a slow drain into a failed one. That is exactly why we look with a camera first, and on fragile pipe we will recommend lining instead.