Charles Bishop writes:

No septic tanks. Someone said the chemicals will only kill the roots at
the bottom of the pipe, not the ones near the top. Is this the case?

Flood the pipe when using chemicals.
The roots are looking for water.
If the pipes normally have an inch of water in them
that's where the roots will be.

Someone mentioned that you could kill a tree.
Once or twice a year, I think you're just going to
kill part of the roots. The tree can survive that.

--
Dan Espen