Stuck bath plug hole - how to release it?

[psonice]

I'm replacing the taps & plug holes etc. in an old bathroom suite, and have an evil stuck plug hole in the (plastic) bath. I've removed the waste from underneath, but the plug hole itself is refusing to budge.

It's the type where the plug hole has the threaded part that drops through the hole attached, and it's fixed to the bath with a large nut & washer underneath. I can move the nut using a large wrench, but the plug hole is spinning round with it so it doesn't actually unscrew.

I'm unable to get enough grip on the threaded pipe below the nut with a second wrench, and I've tried wedging a thin spanner into the top of the plug hole and supporting it with a bar, but the spanner bent before the nut moved. I've sprayed plenty of WD40 on the nut too.

Any suggestions to remove it without destroying the bath? I thought perhaps there's some kind of tool to properly grip the plug hole at the top, or perhaps a thin spanner to grip the nut instead of the wrench? Maybe then I'd have enough threaded pipe below it to get a better grip?

[plumbbob]

Generally the only way to release it is to cut through the nut with either a hacksaw or if you like to live dangerously, an angle grinder.

[psonice]

Yeah, I considered that. The catch there was that there's a wooden panel supporting the bottom of the bath, so the nut is recessed and not really accessible. I doubt there's a hacksaw small enough!

I sorted it in the end though. I had to drill through the plug at the top, so there was a hole big enough to wedge a wrecking bar in. Then with somebody holding that, me with a wrench underneath, and about 3 hours of swearing and broken metal later it was off. It would have been easier to replace the bath, but hey! :)