Flushed and drained properly, there's no sediment left to "filter" out. The sediment built up most likely because the anti-rust chemicals in the coolant were worn-out anyway. The coolant was defective, so "saving" it is counter-productive. (It's possible you have corrosion problems due to improper grounding; but you'd be seeing any aluminum components rot out first, before the iron.)
The flush water goes on the street in front of your house; or perhaps on your lawn, because you've previously drained 98--99 percent of the anti-freeze from the radiator and two block drains for appropriate disposal. Iron dust particles and a trace of antifreeze dilluted by gallons and gallons of fresh water is meaningless in terms of pollution. Depending on your soil, iron dust could be considered a fertilizer. Some places have too much iron in the soil, some places not enough. But in any event, even an engine with terrible rust isn't going to put so much in the dirt as to be a problem.
"Appropriate disposal" of used antifreeze can--depending on your local ordinances--be as simple as dumping it into the sink, or down the toilet. The wastewater treatment facility can deal with the antifreeze; certainly better than allowing it into a storm sewer with no treatment at all, that leads to a river. Most places have actual anti-freeze collection places. They can be privately owned, or set up by "The City". When they get enough used coolant, it's sent off for recycling/processing; or disposed of in an environmentally-friendly way. When there's a collection/recycling option, the City probably doesn't want you dumping into the sanitary sewer system. And you wouldn't want it in a septic tank, either.
The flush water goes on the street in front of your house; or perhaps on your lawn, because you've previously drained 98--99 percent of the anti-freeze from the radiator and two block drains for appropriate disposal. Iron dust particles and a trace of antifreeze dilluted by gallons and gallons of fresh water is meaningless in terms of pollution. Depending on your soil, iron dust could be considered a fertilizer. Some places have too much iron in the soil, some places not enough. But in any event, even an engine with terrible rust isn't going to put so much in the dirt as to be a problem.
"Appropriate disposal" of used antifreeze can--depending on your local ordinances--be as simple as dumping it into the sink, or down the toilet. The wastewater treatment facility can deal with the antifreeze; certainly better than allowing it into a storm sewer with no treatment at all, that leads to a river. Most places have actual anti-freeze collection places. They can be privately owned, or set up by "The City". When they get enough used coolant, it's sent off for recycling/processing; or disposed of in an environmentally-friendly way. When there's a collection/recycling option, the City probably doesn't want you dumping into the sanitary sewer system. And you wouldn't want it in a septic tank, either.
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