On one hand, it’s so easy to do when I’m changing to a new set. On the other hand, I worry about the chemicals (not sure what they’re made of) and the effect on wildlife – does it attract fish and so forth?
General rule of thumb from plumbers: If you wouldn’t put it in your body, don’t put it down the drain.
Don’t do it.
The good news is that unless something is very wrong, they’ll never end up where wildlife can get them. The bad news is that the lenses themselves will block up a pipe where the sewage is treated, and have to be removed.
If it’s your septic system, you get to do it yourself or pay someone. If it’s the sewage treatment plant, they do it, and the added expense means higher water/sewer rates for you.
General rule of thumb from civil engineers: sanitary sewers are not intended for trash, and your toilets and sinks are not trash receptacles.
Sanitary sewers are designed for human waste, toilet paper, and wastewater. That’s it.
Its probably less ok to let 'em go in the sink drain, than in the toilet
Either way, they end up in the same sewer lateral leaving your house and the same sewer main in the street.
They’re disposable, but I don’t believe they’re biodegradable. They’ll either end up in your septic tank (requiring removal and transport to a landfill at a later date), or they’ll get sifted out of the stream at the sewage treatment plant (adding to operating cost) and taken to the landfill.
Skip the intermediate steps and related costs: send them directly to the landfill (put 'em in your trash can).
I wouldn’t do it, but I can’t really see that this will cause serious problems – it’s not like tampons, which swell up enormously and are tough. Disposable contact lens are relatively small, made of hydrogel plastic, and won’t swell past the point where they’re fully hydrated. They’re tougher than they look, but they’ll shred apart eventually. Like jellyfish, they’re mostly water, and when they dry out there’s not a helluva lot left, and that gets reduced to powder pretty easily.
In short, I can’t see these blocking up someone’s sewage system and causing disaster (as happened to the condo of a guy I know when someone flushed a tampon down) unless you’re flushing a HUGE number of them down at once.
I think I can say that almost anything I put down the toilet I would never put back in my body.
Is the OP asking about regular disposable lenses – the ones that roughly have the outer diameter of a dime? Unless you’re stuffing multiple pairs down the sink every day, I’m not understanding how this can pose such a huge problem. Yes, it’s plastic…but it’s plastic that’s ridiculously easy to tear. If it gets snagged on the side of a pipe, the next rush of fluid would rip it free.
I used to wear disposable contacts (till I got a job sitting in from of a computer all damn day - now I’m a four-eyes again!) and if you let those things sit out of your eye or your saline for just a few minutes, they shrivel up to practically nothing, like **CalM **said, so I doubt they could cause much of a problem.
That said,
It’s a contact lense. It’s going INTO YOUR EYEBALL!!1! (Well, not really, but close enough.) Besides, we’re not supposed to flush tampons - per a now-4-page-thread - and those go as far into my body as anything will. 
Nobody’s saying to immediately panic if one accidentally gets washed down the sink drain; your pipes can probably deal. But, just as a thought experiment, in your opinion how many lenses would it take to cause a problem downstream?
Because the Deer Island sewage treatment plant (where I’m guessing your flushed contact would end up) serves over a million people. If everybody routinely flushed contact lenses, that’s at least an extra load on the trash and grit screens, and at worst a major problem.
I think to pass the test it has to go in one orifice and out another.
Yes, if they get that far.
I think this comment was referring to the fact that the sink has tighter pipes than the toilet, and the pipes are more likely to already have semi-clogs (mainly hair) that would catch the contact lenses.
If your sewer pipes have such bad thrombosis that a contact lens will clog it up, you have more serious problems that whether or not to flush contact lenses.that pipe will as soon clog up with a twist of toilet paper.
seriously – have you ever handled a wet disposable lens? They’re extremely soft and squishy and slippery. Toilet paper is far more clingy, even wet.
Oh, sure enough. But as a municipal civil engineer, I don’t much care about backups on private property. 
In any event, it’s true enough that a contact lens is not going to cause much of a problem downstream. It’s just a general principal that I always advise people not to think of their sinks and toilets as being trash receptacles. First they’re throwing contact lenses in, then it’s razor blades, condoms, tampons, and dental floss.
One of the things that tends to cause some of the worst problems for wastewater pumps is dental floss. Wads of dental floss often get wrapped around the pump impellers and clog them right up.
Anything that doesn’t break down immediately in water, like toilet paper and human waste, can end up contributing to backups. And if you live in a combined sewer overflow community, like many older cities, in heavy storm events, the combined sewers can overflow, sending everything into the nearest water body. And while human waste will rapidly decompose in the environment, the trash does not.
Here in Minneapolis, they push the same idea by pointing out that our trash is burned to provide energy, while energy must be spent to remove trash that goes into the sewer system.
Good to know. Thanks for the answers, all. I had already been throwing them into the trash just to be safe and will continue doing so.
I used to also flush condoms down the toilet until I actually visited a sewage treatment plant (the one we have is actually pretty cool, mostly using natural filtration ponds and doubling as a wildlife sanctuary). Then it hit me that this stuff doesn’t just get sucked into a black hole; they’re either filtered out or pumped into the bay.
Upon reflection, I think I imagined that the lenses would eventually dissolve in water and harmlessly degrade… why I thought that, I have no idea.
Well, ignorance I didn’t know was there got fought today. For years I’ve been tossing my disposable contact lenses into the toilet. Not every time, but certainly without thinking about it, or even thinking about thinking about it.
As for the condoms, my wife’s grandmother was almost literally embarrassed out of the state of New Jersey over an issue like that. After a few years of marriage, she and her husband (my wife’s grandfather - deceased by the time she started to tell this story) moved from NYC to a suburban house in northern New Jersey in the late 1940s. This house had a septic tank, rather than the city sewers both were used to. After about 8 or 9 months of living there (less than a year), they had plumbing trouble and called in a plumber who traced it to the tank. After only a few moments of examining it he pronounced it completely clogged and showed them the tank’s contents with a smirk, saying, “Well, there’s your problem, folks.”
The tank was brimming with condoms. While I’m sure the embarrassment is magnifying the image in her memory, she says the physical evidence made it clear that they “had been very active” (ahem). It was a new construction house too, so they couldn’t make out like those were left over from the previous owner.
Shortly afterwards they sold the house and moved back into the city. She claims it was because of the commute, but I wonder. 
I have a colostomy. I don’t wish to discuss it at the moment (and it would be extremely off-topic for this thread anyway), but I’m curious what you would make of Colo-majic liners then :eek: They are plastic bags that fit inside a colostomy bag that you can pull out of the colostomy bag when it is getting somewhat full and throw in the toilet rather than using up expensive colostomy bags (which one disposes of by other means). Or, to put it more succinctly, what do you think of plastic bags of shit?
PS I linked to one of their pages that doesn’t play music, to make it more work-friendly. Clicking the Home link on that page will show a little movie describing it, with background music.