I have a stop ground key water valve 4 ft down at a summer cabin that I had to dig down and replace because small spider web size tree roots grew into the weep hole and wouldn't allow me to shut off my water for the winter. It has a weep hole on the side. I can't pour phosphate or anything harmful down the cover pipe that would harm the brass shut off itself or eating the plumbers tape on galvanished pipe.
Someone suggested bleach or vinegar twice a year but I don't see how this can kill roots. Whatever I pour down the drain would saturate the dirt around the shut off valve and need to kill tree roots. Help?
Mark
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Bleach or vinegar WILL kill roots, although bleach will do it faster.

I'd worry about anything harming the plumber's tape though.

Then vinegar only.

So you are saying just use white vinegar?

Any vinegar will do.