To prove if the problem is in the tank strainer, swap the supply and return fuel lines in the engine bay where the rubber fuel lines connect to the steel ones. This will bypass the strainer and allow non-strained fuel to go to the the prefilter. Any improvement in performance is likely to be due to the strainer blockage being bypassed.
In this situation, the prefilter may block rapidly, so be aware of this issue.
If you want to empty the fuel tank, you can pump from the return line as it goes to the bottom of the fuel tank.

Regards,
Tony

__________________
Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.