Our house exterior is being painted with Sherwin Williams latex exterior
paint. Our painters insist on dumping their paint rinsing water etc. on
the ground. I've heard this is not good for the environment and I don't
want to create a toxic waste site in my yard. They say it is ok because
it is Latex, not Oil paint. Pouring it down my drain would be
equivalent, because of the septic system leach field.

Who's right?