Black tank Problem

[Deluxe21]

I had a leak coming from the toilet so I removed it to find a large problem. The fitting that seals the tank to the toilet has rotted away. Is this able to be replaced or am I in need of a new tank? I think the tank and toilet are the original units and would like to keep them if possible. The tank holds water and the toilet works fine so all I need to do is get them together somehow. The hole is quite a bit smaller than the norm so I don't think the household 3in flange will work. Also I don't know if it would use a o-ring, wax ring , or gasket. Any help would be appreciated.

Thanks
Steve

[Silvertwinky]

Deluxe21,

If I remember correctly, when I took up the floor on our 68 Safari; the part that sits above the floor screws into the tank. This might be the case with your fitting. If it is then you might be able to unscrew it and then you just replace it with a newer part.