Ok I had to remove the plug tubes from a 3S-F. The only way I managed to get them out was to drill a hole through them and use a rod to unscrew them.
Ok this means that they can't be reused so buy your new ones before you do the job.
Most important, make sure you put the spark plugs back in and do them up. as there will be metal shavings going down the tube. I used a vacuum cleaner to suck the shavings out before removing the spark plugs. allso make sure you collect ALL the shavings from around the outside of the tube to, you don't want it to get into the oil gallerys.
This worked for me, but if anyone has a better idea by all means let us know.
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