If you think there is anything in the engine, it is best to take it apart and then flush everything with fuel. It will be much more likely to get rid of anything than just attempting to flush the engine without disassembling it.

What is worse, having to take a few minutes to take the engine apart and clean it, or having to replace the piston/sleeve/crankshaft because dirt got into the engine. I think everyone knoes the answer to that. Better safe than sory.