OK, I am going to chip in here on this one.
First off, I am a chemical engieering/environmental consultant - on this topic, currently the national metal finishing resource center's NMFRC.org ask the waste water expert. (
www.nmfrc.org/ateww.cfm )
First let's seperate the question of what to do with waste 50/50 antifreeze from the question of the chemical flush solution from the question of the final rinse water flush (tap water rinse flush).
Also let's seperate the issue of an individual car owner, DIYer from a business or commercial operation, repair shop, dealership or fleet owner.
Then we need to distinguish between local regulations and national EPA regulations.
For the purposes of this thread I am going to deal mostly with the individual jeep owner DIYer question, as business owners, automotive shops, dealerships and fleet owners are much more heavily regulated and watched than a once every five year DIYer.
The next question is what does EPA say. In general, EPA does not regulate small quantities like a few gallons of, let's call it individual car owners waste, at the individual DIYer level. They have chosen over the last 20 years to promote and educate the public of the need to properly handle and recycle automotive waste fluids, like used antifreeze rather than tightly regulate it at what is called the "waste generator" level. They do tightly regulate the actual collection sites and recycling and disposal sites due to the volumes they handle as well as commercial repair facilities that generate these same wastes.
When you get down to the local city level, the individual DIYer regulations for disposal can vary widely, from nearly non-existent (meaning they just promote recycling) to serious fines for improper disposal and handling.
So, now let's get down to the individual wastes, the used antifreeze, the chemical cleaner to disolve and remove calcium, silicate and rust deposits, and the mostly water rinses.
First, let me say that antifreeze formulas have changed a lot over the years. At one time, as I recall, it contained extreemly toxic hexavalent chromium as a corrosion inhibitor, at least in some formulas. The industry switched to much less toxic, non-carcinogenic replacments for Hex chromium well over 25 years ago (as I recall). Because coolling systems can leak suddenly (like a car accident) or from a busted coolant hose...etc., leaks into the storm water systems from leaks into parking lots and roads do happen. When it does, its no big deal. In limited quantities todays antifreeze formulas (especially the environmentally friendly versions!) do not present a long term environmental problem when released into the environment (in small quantiities! that is) like the old hex-chromate formulas did. Todays formulas are mostly biodegradable now. Now if the antifreeze had toxic heavy metals in them like mercury or lead, then it would be whale of different story! Luckily they do not contain these persistant environmental toxins.
So for used waste antifreeze the best choice is to capture it and carry it to a recycling center. The next best option is to take it to a disposal collection center. Many retail stores that sell antifreeze and oil will accept (for no charge) the used oil and antifreeze back if you can show a proof of a recent purchase of the new oil or antifreeze or other fluids. Barring an acceptable place to recycle or disposae of the antifreeze, most major municipal POTWs (Publicly Owned Treatment Works) can handle very small SLOW flows of used antifreeze with no problem, because it is biodegradable in small doses.
Or said another way, given the choice between letting it leak on the ground or colecting it and and flushing it down the toilet, I would choose the toilet flush to a POTW since it would get treated before it is released to the environment, over letting it leak on the ground. That said I do not recommend used antifreeze disposal via the toilet and definately do not recomend disposal on the ground anywhwere.
In many areas toilet flushing disposal of used antifreeze may even be illegal, depending on the local POTW ordinances. If you have a septic waste water system I would not use the toilet as it will probably overload the septic system and kill the waste water bugs that treat the sanitary waste in the spetic system and lead to expensive repairs of the septic system. The same goes for small rural POTWs that have small waste water flows. One gallon of antifreeze in a 100 MGD (Million Gallon per Day) WWTS (Waste Water Treatment System) in a big city is a far cry from a gallon going into a 50,000 GPD local subdivision WWTS. So what your toilet is connected to affects the viability of using the toilet.
Next is the chemical cleaner used to remove scale, corrosion, rust etc from the cooling system. This one depends on the chemcial used in the formula and its concentration, and pH. I would check with the cleaner manufacturer to see what is in the cleaner formula, is it biodegradable, is it safe for POTW disposal, can it be neutralized with baking soda to make it pH safe for POTW disposal, is it like dish water and cloths soap waste water and thus safe for POTWs and septic systems? It may be! Is it safe for Septic system disposal? Is it biodegradable? Can't hurt to ask!
I would not recycle used cleaner solution as used antifreeze! It is not the same stuff and can cause problems for the collection centers that are trying to recycle just the antifreeze.
So that leaves the flush water used to flush traces of used antifreeze and traces of used radiator/cooling system cleaner solutions. I see no problem with the DIYer using the POTW or septic system for the fresh water flushes if the antifreeze or cleaner solution has already been drained and collected seperately. A good flush might be 50 gallons or more, and thus would be mostly water. In fact the rinse water is probably cleaner that the wash water you dump in your driveway when you wash the outside of your Jeep! Especially if you are into MUD!
Once again, this is only about the indivdual DIYer doing a once very 4 to 5 year drain, flush and replacement of antifreeze that does not have a local collection site available for recycling and disposal of used antifreeze and used cleaners. I would not make these recomendations to anyone changing fluids for a fleet, or a dealership or repair shop, etc. They have a much more difficult task and long list of regulations they must comply with.
Also, NEVER, NEVER, NEVER, use the toilet for any of the other automotive fluids like motor oil, tranny fluid, brake fluid, power steering fluid, or differential fluids, always collect and recycle them seperately! Also, use seperate containers for them, never mix these different fluids in the same container or the recyclerss will probably not accept them.
Here are some links to some sites on the subject.
http://www.greentruck.com/waste/antifreeze/1102.html
http://es.epa.gov/techinfo/facts/alaska/ak-fs19.html
http://www.epa.gov/epaoswer/hazwaste/id/antifrez/index.htm
http://www.epa.gov/msw/antifree.htm
http://www.eetcorp.com/antifreeze/antifreeze-faq.htm
