I have had algae in my older wagon, and when faced with removing the fuel tank I elected to avoid that because of the self levelling valve. I had a bad experience with this valve once, the arm that attaches the valve to the cross bar (the bar that sends it motion information) came loose, I believe the mechanic that last worked on it failed to tighten the locking bolt.

I was driving along and the car was instantly forced to ride with the hydro shocks at the maximum "up" position. It was pretty scary at 65 MPH, with the car bouncing incredibly. It was really a white knuckle ride because I was not expecting it to happen.

But what I was burned over later was, after I reset the arm I thought everything was fine until I noticed my rear end was quite a bit higher than normal, and by that time I had put maybe 1000 miles on the car and worn the inside edge of the tires. I had to replace two almost new Pirellis because I didn't catch it in time.

If you remove the hydro valve, be certain to set the height of the back of the car properly, using a measuring gauge. Or take the car to be checked at a dealer or good shop that knows the procedure.
And you don't want to poke the hydro valve arm without putting jack stands under the car or having it on a hoist, lest it drop down on you when the valve releases pressure from the shocks.

FWIW, I flushed the fuel tank in the 300TD when it was almost completely empty, in the vehicle, using Biostat and Red Line Diesel Catalyst to loosen up the dead algae, I drove a while on new filters with a quarter tank of the mixture in it. Then I drained what was left ( about 2 gals) If you don't have a large pan to catch the fuel you will find it kills vegetation quite well!

The only fuel tank I HAD to remove was a rusty one in a W115 (gas, not diesel) that was ultimately recoated at the local radiator shop successfully. That tank was easy to drop, compared to the wagon.

Dieseldiehard
1971 220 (gas) 4-spd manual 104041 or is it 204041?
1979 300TD w/ ’85 turbo engine 288975
1983 300D 237300
1985 300TD 205437

I've heard folks suggest taking fuel tanks to radiator shops to be cleaned. How receptive are these shops to the idea of throwing a dirty fuel tank in their cleaning baths?

M.

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He's wild and free and so close to it only Gunk will clean his fingernails!

All it takes is money, ask them! Not a bad idea that. You might even have it painted too! My 115 tank looked like new and its still in service, the new epoxy based coatings (it takes three coats) do stop rust.
Dieseldiehard