Use a breaker bar and if needed a pipe extension on that. That's the only way I've ever been able to get it. The thing that sucks is that the square is larger than the drive that fits in it, but too small for the next size up. I haven't done this yet, but I've thought about buying a cheap breaker bar one size up from the plug size, and then grinding the thing down so it fits snug into the plug. It'd be worth it because those drain and fill plugs get all chewed up when you take them out and it'll suck when the day comes that you can't back them out because they're too far gone. I'd say, just buy a bolt of the same threads and put that in instead of the plug, but I'm pretty sure the plug is tapered pipe thread, in which case a bolt wouldn't work. A person could also buy a short bolt of the right diameter and square it on the end and use that like an adapter to take plugs out, or JB weld it into the plug.
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Rob '93 SE-R
PM or e-mail me for Progress swaybars $190 shipped, B13 Progress coilovers $1300 shipped and B13 Progress LCA brace $160 shipped.
If the plug isn't damaged beyond hope, make shims out of soda cans to take up the slack around the ratchet/breaker bar lug, then use additional pipe for leverage if needed. Mine was a struggle even though I was the first one to attempt its removal since the car was built.
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Bruce in Houston
'94 Nissan Sentra SE-R w/ $tuff, converting to ITA
'98 Suzuki Bandit 1200S w/ $tuff
'02 Dodge Dakota SLT 4-dr tow beast, stock!