Might depend a bit on what you mean by "just dump contents". Do you mean something like a once and done scoop out? Or what kind of tank use?

There's stuff like composting toilets or toilet vaults built for composting on a small scale if that's the sort of thing you are looking for. For something like a summer cabin perhaps?

OK, it's better not to do it. Yes, they do pump the contents of a septic tank for €90 and take it away.

Assuming you're in the EU, I'd be surprised if it wasn't illegal (VERY illegal, like substantial fines and penalties) to pump out on your own.

90 Euros is a quite reasonable price, especially since you only need to do this once every couple of years at most. The company doing this probably has to pay at least half that to 'tip' it at the sewage treatment plant.

And it's very important to do once in a while - it's the sludge at the bottom that builds up, as well as layer of floaty scum at the top, that can wreck your leach field if it builds up too long. And the pumper will usually take a look and tell you how it looks/if any obvious problems, especially if you ask (although won't always be a formal inspection). You can ask if it looked full (of sludge); there are rules of thumb for how full is too full.

Some will say you can do this more infrequently, but I reckon it's not a contest to see who can pump their tank less, but how long your system lasts. Redoing a leach field is not fun, it means ripping up the yard.

People say it does not need to be pumped out at all since bacteria eats it. In the EU it is a concrete "tank" of 2 sections with additional tank further for liquid release.

You can compost septic tank sludge but what you've described (pouring it into a ditch) is not composting...

Getting the right ideas. Pour slowly and mix with organic materials such as saw dust, leaves, soil, compost etc. During childhood we used to dig a hole, poo in it in the garden, throw compost etc.

"People say it does not need to be pumped out as bacteria eats it." This is wrong but with a grain of truth. In all such systems, the first tank allows settling of what I'll call sludge. The grain of truth is that bacteria eats and consumes SOME of the stuff in the sludge and this reduces the volume of that sludge significantly (similar to the way composting reduces volume, or alternatively a wood fire miraculously gets rid of so much wood). Some escapes as gasses, some dissolved or suspended in water that comes out later in the system.

BUT: there is always, always some stuff left behind. Either organic compounds that can't be reduced further, or smallish amounts of non-organic stuff (think of even just grit or sand from washing). It builds up over time, and if there gets to be too much, it can start to harm the way the system works. This might mean a leach field being overloaded and ruined, or that water coming out of the system is dangerous and can harm the environment, or other bad outcomes.

Now some will argue how often that first tank needs to be pumped out. There's no single answer, it depends on conditions, usage, temperatures, etc etc etc. My point is that a given system may only "need" (strictly, based on how full it is of solids) to be pumped out in seven years, it's actually hard to know exactly when, and the consequences of not doing it before it gets too full are pretty bad. So pumping out once every couple or three years (esp if not expensive as in your case) is just more prudent.

That said, if someone wants to argue that their own system is lightly used, large, they check it from time to time, are very careful about what goes in it, and whatever other mitigating factors mean they only have to pump every 5 (or 4 or 8 or whatever number) years, fine, I'm not going to quibble or argue about someone else's choice if they know the risks.

But I don't think anyone can reasonably argue that it never needs to be pumped out (well I guess unless they just plan on replacing when it stops working).

Ok, so it's not something like a one and done cleanout of something like a summer cabin. You seem to be talking about regular emptying of your regular household tank.

I'm not in the EU.. But in the U.S. you can't just let your septic pump out like that. You can have a leech field for distributing the liquid, but your septic tank has to be pumped out and removed by a service, you can't just dump it yourself.

Depending on the size of your tank and how many people you have in your household, how often you need your tank emptied will vary. There's also stuff you can flush into your tank to help break down the solids.