Roots blocking drain

I have started digging up a plant that I suspect is growing into my drain and causing it to fill up then drain away. Not completely blocked yet. I dug down to the clay layer, but I suspect the drain is too deep for me to reach easily. Should I just chop of the plant root at the clay layer and fill the hole? I suspect it will die like that, as it will have no sunlight to encourage new shoots. Or should I keep digging and try to find the drain?
Thanks

Get some Tree and Blackberry Killer from Bunning and paint it all over the stump.
I have seen tablets that you can flush down a drain to kill off roots as well;
https://www.bunnings.com.au/drain-clean ... lsrc=aw.ds
See how that goes first?

Do you remember the names of the tablets?

Drain Clean Root Control.
Available at Bunnings.
It's basically just copper sulphate.

Tnx alot.
i have an issue with a client of mine, i'll check your solution.