The easiest way is to remove the camshaft so that all the valves are closed. This would require removing the timing belt.
Then you can clean away and vacuum what's in there. However, it's possible that liquid can still leak down so after the camshaft is back on and the intake back on, I suggest removing the glow plugs and cranking the engine to blow out any possible stuff that had fallen in. It doesn't take much liquid to hydrolock a high compression engine with a tiny combustion chamber.
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