I've had this 1993 C180 sitting on my front yard for around 6/7 years now. It hasn't been started in 4 years, and when I tried to start it a few months ago, I got a perfect crank but no ignition.
I decided to try and get it running again. I am by no means a mechanic and have 0 experience working on cars so I have only tried a few solutions. So far I have only:

-Replaced the 4 spark plugs
-Checked engine function by adding starting fluid into the throttle body. The engine turned over and briefly ignited before dying.. suggests that the problem is in the fuel system
-Added ~10L of new petrol
-Attempted to drain petrol (from sending units) with no results.

I discovered a few weeks after adding new petrol that the car was left with at least 1/4 tank of petrol inside. I suspected that the petrol would be filthy by now, so I wanted to remove it. I tried to drain the fuel by opening the check valves on the fuel sending units, but that yielded only a small dribble of petrol per sending unit. Nowhere near the 1/4 + 10L of fuel that should be inside. Any petrol that did come out was a very filthy and opaque brown colour.
I did some online research and found that, as the fuel had been left in the car for so long, it would most certainly have turned into "jelly" that would clog up my fuel system, preventing fuel from reaching the engine.
I now have the task before me of removing this stuff from my fuel system. I have seen some people rinse out their fuel tanks with caustic soda to get rid of it. However, I understand that this MB has a strange dumbell-shaped fuel tank with a venturi made of plastic that moves fuel from each tank side, and this will probably disintergrate if I added caustic soda, which will require yet more unfamiliar work to fix.
I understand that removing the fuel tank may be unavoidable, but I would like to try every other possible solution to remove the jelly before I do this.

I really don't want this otherwise perfect little car to go to waste. Any advice on this would be greatly appreciated

To help others, let's be clear about what you have.

You have a 1993 W202 C180 with M111.940 1.8L four cylinder naturally aspirated petrol (gasoline) engine. Petrol, not diesel, correct?

You have not yet sufficiently demonstrated the fuel tank, fuel pump or fuel are problems.

spoiler alert: all cars since the last 30 years have fuel tanks ask you describe, with two lobes and a transfer pump.

The following steps are given with the idea that you want to operate the car with relative frequency. If you omit any step, it would mean sliding down the slippery slope towards a bodge job. Don't do a bodge job. Rather, sell the car.

You need diagnostic tools for this job, at minimum: a multimeter (digital voltmeter), cylinder compression gage, and fuel pressure gage.

0. replace spark plugs, vehicle battery and ignition coils and wires.
1. confirm fuel pressure is present at the fuel rail. If not, diagnose a weak or failed fuel pump, or clogged fuel lines.
2. If pressure at the fuel rail, confirm fuel is getting through the injectors by removing spark plugs and observing fuel smell. Observe injector clicking during cranking. If not, diagnose clogged or failed injectors.
3. If the above tests are good, I would start replacing sensors. Manifold absolute pressure and crankshaft position sensor would be first.

Others will give more input. Replace the battery, spark plugs and coils, try cranking again and report back. Then come back to the fuel pump diagnosis if necessary.

Some money needs to be spent on this car to get it back into service.