Most properly sized and installed septic tanks do not ever need to be pumped out. They compost on their own and the excess water seeps out underground.

Actually, a proper septic tank (according to EU regulations) has to be water-tight and be emptied regularly. Many beaches on the Mediterranean loose their health pass occasionally due to nearby overbuilding and improper septic tanks.

That's not a "proper" septic tank. That's just a holding tank. The word 'septic' alludes to the fact that you are promoting putrefaction to decompose the contents.

RVs have holding tanks that must be emptied. Thus, they aren't called "septic tanks".

But I'm sure the term is used loosely.

That's not the case in the US.

At least, it's not the normal case in the U.S. We call that a "holding tank", not a septic tank.

However, if the system isn't maintained it often needs replaced at a large expense. Most homeowners don't know how to inspect and don't bother to hire someone knowledgeable.

Our local township has an ordinance where every residential sewage system (10k residents, not sure how many systems that is) has to be pumped out and inspected by a certified sewage hauler. This way, the homeowner knows about and is required to make simple repairs before the entire system fails.

this was contrary to my city-dweller's understanding, so i did some quick wiki-reading and it seems like the reality is somewhere between you and GP's statement? i.e. they do biodegrade waste via anaerobic bacteria, but non-degradable sludge has to get pumped out every few years.

Your city dweller’s habits compel you to throw fat and oil down the drain. These need very high temperature to compost. But then you are also throwing chlorine and ammonia based cleaning agents, which greatly inhibits organic life.

If you let the fat and oil solidify at room temp and dispose of them in the trash, and if you use regular soap in the recommended amount, and if you septic tank additive once in a while, you will be tearing the problem at the source, and will only need to take care of the tank when it’s time to replace it in 40 years.

This is why you see a jar full of bacon fat and the like in lots of rural homes. They aren't saving it to cook with, they are collecting it to throw out with the trash instead of sludging up the drain and septic system. People are much more careful about what they flush down the drain when they know they will be responsible to fix it if they cause issues.

For the apocalyptic end results of lots of city dwellers flushing non-biodegradables down the drain, Google "fatberg" - only if you have a strong stomach.

It depends on how the tank is setup and the drainage system it has.

Septic tanks are not closed systems they are open and intended to provide an environment that can produce a bio-reactor while maintaining drainage through the soil.

Many good systems don’t need to be drained other than every few decades in fact good systems would outlast the tank and the filtering substrate it’s built on so when the time comes you need to dig out the tank and the gravel and other filtering particulate it used because that is what has degraded.

The problem with septic tanks is that they don’t scale we’ll have one on a large property in the middle no where that 5 people use and it’s a great solution have a bunch of them and worse over use one in particular and you get a polluting mess.

But septic tanks also don’t solve the other problem with western toilets and that is the amount of water they consume which is simply unfeasible for many developing regions.

TLDR; if the septic tank was installed and sized correctly it will outlast you even without pumping it, but it’s not a solution the reason we don’t use them in cities is because they don’t and can’t scale with urban population densities.

Also, some US states are encountering issues with bio contamination in their aquifers and as water issues become more prevalent (perennial droughts in some states shrinking aquifers making them less resilient to contamination; perennial flooding in others moving the water tables closer to septic tanks and making them more prone to contamination), the requirements to isolate septic tanks from local ecologies will only grow (ie, increasingly more counties will require to close them, watertight protect them, require them to be regularly pumped moving forward, and/or replace them with a connection to nearby sewage systems).

Yes the ground water level, soil permutability, distance to water sources etc. has a lot of implications on what sceptic system you can implement and I would bet that many tanks are put in without much regulation or oversight.

Other areas like those in which ground temperatures drop below freezing for long period of time might also require tight tanks and constant pumping since the cold may stop the reaction in the tank so it would surprise me if tanks in places like say N. Dakota would be pumped year before winter to prevent them from freezing shut and overflowing.

>every few years

Every few decades for a properly sized and properly functioning system.

Septic tank owner here. I own a single family home, maybe larger setups are different. The recommendation from the installer is that it is pumped and inspected every 3-4 years.

> The recommendation from the installer is that it is pumped and inspected every 3-4 years.

That sounds about right if the goal is to keep a system that's not properly functioning (not enough microbes to break down solids) from filling up to the point of causing problems. You won't go wrong if you follow that advice but depending on what goes into your septic (do you have a garbage disposal, do you do laundry with bleach, number of people in household, etc) you may be able to go an order of magnitude longer. Recommending a system be pumped every 3-4yr is like a 3k oil change, it's excessive in the overwhelming majority of use cases but it will make more money for whoever does the work and not cause a system to fail in a way that comes back to bite whoever installed it.

The manual for the original Nintendo Entertainment System said "Do not operate continuously for more than 15 minutes."

Sometimes legal departments force them to include those recommendations in order to err on the side of "absurdly overcautious." And sometimes the recommendations are merely prudent! I'm not saying you can wait longer, just that installers may have a motivation to exaggerate.

But unlike an NES system, if your septic tank develops a problem you now have liquid and solid waste flooding your yard and home, and your toilets, sinks, and showers are useless until it's fixed.

I feel like the failure mode for electronics is "randomly catches on fire" which can be just as devastating, if not moreso. Nobody has ever died because their toilet backed up. Their house burning down in the middle of the night is a different story.

People die from diseases caused by sewage, but it's usually a downstream issue.

My grandparents had there's installed in 1983. I think it was a somewhere between 700-1000 gallons. The toilets finally stopped flushing properly in 2010. It was because the tank was completely full of sludge. They got it pumped, and I guess it'll go another 20+ years now...

Where does all the solid waste go? Unless you mean they are big enough where they'd need replacement before needing to be pumped.

That makes no sense. What happens to the solid material?

What solid material? Fecal matter, toilet paper, small food particles, etc break down in a septic tank.

I suppose there will be very small amounts of minerals that don't break down but they are insignificant.