It sound like you have a really dirty tank. I would suggest hitting it with some alge-side. but if you have a lot of that stuff it would be best to just remove the tank entirely and clean the entire tank. it sounds like you are treating the syptome and not the disease.
-stephen

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68 250s SOLD
78 300d non turbo SOLD
1980 240d manual SOLD
1981 300SD 360,000 miles I think she's doomed for a parts car but has a good engine SOLD the engine to spamman
1977 300d non turbo SOLD
1985 300SD california car
1978 240D Manual