I would wait to do the job when the reserve light comes on, less than 2 gals that way (I had a bad experience with spilled fuel as it kills grass!)
Having a sack of the cheap kitty litter on hand to catch what does spill is also a good idea.
In the TD there is an internal socket that is about 1-1/8 in (30 mm?) and differs from the sedan, at least thats what I remember its been over 12 years ago that I had a case of algae. I used a strong dose of RedLine Diesel Catalyst too with the Biostat to help loosen up any algae that remains in the tank.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body. '87 300D w/ Sportline suspension. No more '79 300TD w/ 617.952 engine at 367,750, it was my annual driver to Texas and I sure don't miss it poor A/C heater system!