How do you dispose of the lye/water/mimosa mixture the safest way with the least harm to the earth and to our water supply?

dont get rid of it. EXHAUST it. use everything you can on it!! get all the good stuff out!!!

I just keep it in my disposable jug, ducttape the lid, cover it in a plastic bag, tie, and set in trash...not the most efficient method..but I dont want that to spill anywhere in my house.

i just flush mine down the toilet.

The lye stew is fine to go down the drain... the most common use for the stuff is as a drain opener.

Be careful though! Filter the bark out of it with a coffee filter(wear gloves and goggles, have vinegar nearby in-case of spillage). Pour the water down a cloggy drain. Compost the bark(neutralize with vinegar first), bury it whatever you gotta do. That's at least my idear.

I've heard of a user here, dumping the lye slurry down the drain with the MHRB in it and having to call a plumber.

Try explaining why there's crushed purple wood in your sink/toilet/shower, might raise some suspicion.

Toilet! All ways a good place to dispose of the stuff

With limtek, the leftover material would be solid and can be disposed of safely as such with no worries about corrosive chemical properties. SWIM believes the toilet to be the best bet, otherwise.

Down the drain.

As mentioned above lye is used as a drain opener. It's not toxic to the environment, it's just very alkaline but when diluted doesn't cause harm.