When people use the toilet on planes, the design of the toilets uses so much less water than a toilet on the ground, in the airport, and how much a flush of water takes.
So if you assume that people were going to use the bathroom regardless, they just saved the processing of a lot of water by doing it on the plane. Probably ounces versus gallons. (~100 mL vs. 1-2 L)
(parenthetical note, sometimes I wonder if a vacuum toilet would become available for home use, it's so effective!)
Now certainly, flying around to use the bathroom used up a lot more energy, but regardless... Also, you might ask whether people tend to drink more than average because they're offered drinks on a plane.
I used to wonder, considering the hundreds of pounds of water/soda/etc loaded on a plane, as people drink and consume it all, wouldn't it be efficient for the plane to dump that water in flight and save the weight and extend the range. Turns out (of course) that is so negligible compared to the overall weight of the plane...
I've heard it said that plumbing issues dramatically increase with modern, water-efficient toilets. It's not hard to imagine why. Sewer usage and maintenance are at a far lower rate, so stool will settle and clog when ever smaller amounts of water are introduced.
I'm not sure this problem can be solved, assuming regular sewage as the method of disposal.
A new building with new toilets should work very well. Replacing your toilet may not help if your pipes from the 60s are basically nonexistent.
However I mean non alcoholic drinks of course, alcoholic ones dehydrate even more. I rarely drink alcohol on planes for this reason. But this is often what people drink because it's free.
Edit : Writer of the article also thinks that.
>> The world’s busiest airport by passenger volume, Guangzhou, could have handled 5.14 million litres of pee in April 2021.
That converts to about 43k 55-gallon barrels per year, or about 118 barrels per day. An insustry standard oil tanker truck is about 210 barrels, range 50-300 [0]. So, all in all, pretty manageable.
[0] https://www.reference.com/business-finance/capacity-tanker-t...
My rule is to eat and drink as little as possible before a flight, ideally not eating at all. If I do eat, hopefully it's high protein and low in fiber. As a result I usually don't need to use the lavatory, which is nice because it has made me much less apprehensive about getting a window seat.
I wish more people had this mindset. On so many flights I've had, seemingly half the plane is ready to take a shit. My only explanation is that they're overnourished on the Standard American Diet. Imagine how much less waste would have to be pumped out of airplanes.
A lot of folks poop on a schedule: Making sure you don't poop on the plane might very well involve adjusting food for a few days before a flight, depending on how often you poop. Some folks poop multiple times a day, some folks poop a few times a week. Some women poop more during their monthly cycle, too - which, by the way, does not happen at the same time every month nor do you always have notice.
You'd be able to eat not too long before the flight, though, if you are healthy simply because most folks don't process food too terribly fast (but the timing varies). Adjusting what you eat for days just isn't worth it, and not everyone can do this.
Also, not everyone on the flight is going to be American, but the chances are higher if you are taking in-country flights in the US. I personally don't encounter many Americans on flights - I'm often the only one. But then again, I don't live in the US either.
If you're not used to flying (like yourself) this might be the case. For regular flyers (like me) it's often more like taking the subway or commuting to work. Personally I always get an aisle seat, take at least two liters of water with me to combat the dehydration and let me get to work/family/whatever in the best shape I can be when I land. I always eat ahead of time or at the airport (lounges make this more reasonable) because I also know that on the other end of the flight there's baggage, a taxi, checking into the hotel, getting to dinner, etc. So figure at least two hours of hassle before a dinner or snack is possible, usually more.
I've never been on a flight long enough that I needed to eat, but even on a regional flight I find myself wanting at least something to drink because my throat feels a little dry.
Of course, if they dump all their drinking water, it'll be hard to reach the maximum pee capacity per passenger. But you could always resort to dumping food.
15 tons equates to over 10k liters, if you are interested
https://www.thecalculatorsite.com/conversions/common/liters-...
Second, pilots can trim the plane while in flight.
Third, no safety margin is needed here because this is not a safety problem.
The amount of pee that can be deposited into the tanks is limited by the amount of pee they can physically hold at the start of the flight plus the amount of drinks they can consume during flight.
But more realistically, on a long flight, it is just the amount of drinks they can consume assuming they drinks are mostly used to replenish whatever they have peed. Most people try to empty their bladder before flight and are willing to have full bladder when they leave the plane (to relieve themselves afterwards) so I think even this is already a little pessimistic.
On 747-400 you have max 660 passengers. 1135L divided by 660 passengers gives ~1.7L per passenger on average. Which is a lot. Consider this is an average -- some people may drink way more than that but most people drink less than that in a day.
So it seems it might be possible to run out of the tank -- if you have a very long economy flight in a large plane converted to densest possible seating arrangement and if you are willing to believe people will be buying over 1.7L of fluids per person on an economy flight.
Of course, all that calculation goes out the window if you plan to fly an economy flight full of Australian Oktoberfest fans directly from Germany to Sydney.
Sewage overflow is certainly a safety problem. Just health safety though, not flight safety.
1.7L per passenger is a large volume of excretions, but flight operations may require multiple flights before emptying the tank, especially if there's a problem with the emptying equipment at some airport. Would a failure to empty the tank prevent a plane from taking off? Probably only if the remaining capacity is likely to be insufficient.
My informal search [1, 2] seems to indicate that every galley seems to have WC close by, though not vice-versa. Would never have thought to attribute that to an engineering decision before this discussion!
[1] https://theflight.info/seat-map-boeing-737-800-united-airlin... [2] https://theflight.info/seat-map-airbus-a320-200-united-airli...
PS: Also amazing that thanks to COVID, I actually had to look up images of airplane layouts!
On a related note, although the tanks can't be intentionally discharged in mid flight, airline sewage systems do occasionally leak https://en.wikipedia.org/wiki/Blue_ice_(aviation)
747s can fly with an extra engine under the wing. Compared to that, a full waste tank is nothing.
https://www.qantasnewsroom.com.au/roo-tales/that-time-when-w...
From the article: 1 liter (747) to 2 liters (A380) per passenger. More than enough, even if a dozen people manage to catch the runs and eject more liquid.
> how would an almost full tank affect flight behavior
Not that much, pilots can (and have to, as part of weight redistribution caused by the fuel tanks emptying) "trim" the airplane - basically, applying an offset to the neutral position of control surfaces (see https://en.wikipedia.org/wiki/Trim_tab). And all the content of the toilet waste tank was already in the plane before (either in the bodies of the passengers, or in the freshwater tank), so it's only a minor distribution change.
Most likely they use a macerator pump that accomplishes it physically and instantaneously.
Worse problem: cleaning up un-capped, tipped-over bottles that are no longer full of pee after deboarding.
"Tic-tac, sir?"
There's a reason why even Ryanair, otherwise the leader in borderline unethical airline behavior, quietly buried their 2010 attempt to introduce a loo charge [1].
[1]: https://www.theguardian.com/business/2009/mar/05/ryanair-toi...
Charging for the toilet could just encourage those same people to light-up in the main cabin.
Eliminate the bathrooms and make everyone wear Depends. I would not be surprised this happens. The bathrooms could be replaced with a few seats and they save money by forcing people to clean up themselves :)
I now refuse to fly, I would rather drive or take a train or even a bus. Of course with covid driving is probably the better option if you can spare the time.
Of course I heard many people now drive instead of fly, which is making medium travel distances (say under 1000 miles) not enjoyable. Never mind the CO2 being pumped out.
Again the US needs a good public transportation system, which of course will never happen. If pols just stop talking about this, it would probably lower CO2 emissions from all their hot air they are expelling.
