I needed to change a fill valve in a toilet. Got the first (easiest) tank bolt off. The second one has got me PWNED! It's a brass bolt. Flat head on the end inside the tank but it is so worn that you can't keep a bit end in it.

The under side of the tank has a wing nut on it. I have never seen a wing nut on a tank bolt before. I got it loosened some. I can't get the wing nut to budge any further. Now the whole contraption spins. I can't get a grip on the flat head end since its so worn to prevent the spinning. Feels like the wing nut is rusted to the bolt. I already hosed it down with WD40. Hasn't helped.

To make it worse, I think the tank got tightened down while off center which bent the bolt ever so slightly.

This is the side of the tank next to the vanity. Very tight quarters. Very hard to contort over to get a grip on the wing nut underneath and then try to hold the bolt end inside the tank without losing grip.

Any ideas???

Tannerite.

(Sorry, couldn't resist.)

Do you have enough play to get some Vice Grips over the head of the bolt?

use a dremel or trangular file or small saw or something similar.
cut a notch in the bolt, a nice deep one so you can reach in with a nice fat flat-head and have plenty of grabbing room for lots of torque. If necessary, take a driver bit and put it into the appropriately sized torque wrench for increased power. If that don't get it out, you've got two options: If it's in place with a nut on the other side, just grind off the head and knock it out. If there is no nut  on the other side (which I highly doubt), center punch and drill right into the bolt. Keep drilling with larget bits (like removing a rivet from an AK), but once you see rust inside, you know you're in the threading [and if no rust, then the thing must be superglued or melted(?!) in place]. now take a tap and thread right over the remenants of the old screw. Easiest way, if there's a nut on the other side, is just to dremel or grind the head off.

ummm, ya...........................basically what i was gonna say

dremel or hack saw that fucker off

or

go and get a rounded bolt extractor kit, like $30 from craftsman, work good

Agree with cleaning up the screwdriver slot with a Dremel.

A slightly different approach would be to Dremel (or file) two flats on either side of the screw head and than grab it with a Vise-Grip.

While it wouldn’t be the first thing I’d try, if you’ve got an easy-out available, I guess you could drill a hole into the screw head and then use it.

Good luck!

Thanks everyone. Didn't have a Dremel on hand so I used a small hand held file (used for sharpening the lawnmower blade) and file the wing nut off.

What a PITA.