All good answers previously. I also do the bucket of water in the cockpit
with hose filling the bucket. Have hose from water pump
to suck out of this bucket.
A couple very important tips I have learned...
If the bucket is above the water pump (likely), it will continue to siphon and can cause the engine to keep sucking water until the siphon breaks. I found this out the hard way when winterizing with antifreeze. I shut the engine off, lifted the tube and the slug drained into the engine. Found out in the spring when my oil
was milky. Fortunately I checked before I fired it up.
Now I run the bucket dry (either water or antifreeze), lift
the hose up (engine still running) until I can clearly hear the water pump is now sucking air (10 secs approx). Only then will I shut down the engine and know I don't have a siphon.
2 years ago my uncle waterlocked his Yanmar
doing something similar with the bucket and got lucky. Said when he was turning over by hand he could hear water in the cyl.
I ended up needing to change the oil 4-5 times to get rid of the antifreeze. Once boat went in the water, I ran it hard for an hour and then changed again. No issues.