I usually tone with selenium and hold any used toner for disposal when the county has its annual hazmat drop-off day.
This is probably overkill. Selenium toner is fairly innocuous (although I don't suggest drinking it.). And as it is used, the selenium content is depleted, and it becomes progressively less toxic.
I have read that if you have a few rose bushes, dumping the depleted toner around them is a great means of disposal. It's actually supposed to be good for roses.
As to brown toner, the concentrate is packaged in 16 ounce bottles. A typical working solution involves one ounce of the concentrate in a quart or so of water. And since we are at the bottom of a hill, we have a grinder pump that requires that there be a minimum quantity of waste in the reservoir before it is actually released from the house. Practically, that means that the toner working solution will be diluted with at least a couple of gallons of water or other waste.
Our house is fairly new, with toilets that require 1.3 gallons of water per flush. So flushing a toilet puts five times as much liquid into the waste stream as would be involved in dumping one batch of toner working solution.
So based on the dilutions involved, I don't believe that disposal of depleted toner into the normal household waste stream is harmful.