To clean that strainer, plain soap and hot water is required, you will need a new O ring to seal it though - its a large size and available at almost any parts shop with a counter (not hanging on the display shelves)

There would be quite a lot of crud surrounding it in the tank right under the inverted bowl the strainer sits in - dont jam your finger to scrape it off, use a coat hanger fashioned into a tool to move that trash to the opening and let it fall out.

Otherwise, removing the tank is a 10 minute job on a W124 (wear gloves as some parts are sharp back there)

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)