Don’t think that you need anything too harsh or abrasive as in a plastic tank there is not usually any bound on dirt like rust to steel. I would remove the tank, seal off the outlet and add an inch or so of fuel and give it a good swirl round then pour it back into a can via a gauze filter funnel with a bit of blue roll in it as an additional filter paper. While pouring try to keep the fuel swirling to help any debris in suspension. Then have a look at the blue filter and see what may have been captured.
As an aside and not wishing to insult anyone, I used to regularly see people sealing off fuel pipes with a handy bolt. The problem is that the threads act as a rasp and loose of bits of pipe material which tend to fetch up where they aren’t welcome. Other than using the proper clamps, when scrapping an engine I used to save the mushroom cam followers. They are hard, polished and have slightly tapered ends and are unlikely to cause the above issues. Two or three different diameter ones are useful emergency bungs.