Where do you discard chain cleaning solvents/degreasers?

After reading comments that chain cleaning solvents could have substances of questionable health effects, and despite the benefits of bike chain-specific cleaning liquids, I’m doubling down on choosing an ordinary household citrus degreaser for chain cleaning, while ensuring to rinse with tap water—perhaps using a separate run of a bike chain cleaning device—promptly after using the degreaser (then drying for five minutes in the sun, applying a few drops of grease, spinning, and wiping).

I cycle on roads and only mildly dusty paths. My chain doesn’t get grimy. Still, I would like to enjoy the peace of absolute zero noise emanating from the chain (the wind whistling between my ears and the helmet straps will be a tougher problem to eliminate), and so I am aiming for a perfectly clean chain. Also, I am starting to feel, perhaps delusionally, that this little remaining chain friction is what’s standing between me and the "next stage" of cycling (faster).

Where do you discard the liquid when you’re done? A citrus degreaser meant for household cleaning can presumably be safely flushed down the toilet, but this is not an option when it has been used to clean chain grime/grease. The cycling-specific solvents appear to be nasty enough they cannot be flushed down the toilet, even before they’re mixed with dirt/grease.

Just dropping the tiny two ounces / 60 milliliters at the side of the road means the material will make its way unprocessed alongside rain water to canals, which is the worst possible option.

Which leaves a backyard or a garden, not too near any plants that might be consumed. The "bio" indication on some citrus degreasers suggests they can be poured right next to a tree, with little to no harm—but the presence of the grease means that pouring farthest from tree roots is wiser. Can bike chain-specific solvents also be discarded on some grass patch?