The message . com
from "mjbarnard" contains these words:

New modern wc just installed. Close coupled pan and cistern. Pan is
"back to wall" and cistern rests directly on top it. All connections
satisfactory except those joining the pan to the cistern.

These are not the standard connecting bolts and plate.

Two bolts go through the bottom of the cistern and screw into fixings
within holes in the back of the pan. They are designed to do this
without anything between the pan and cistern.

What about the rubber doughnut? That goes between the cistern and the
pan to seal the flush.

Supplied are conical black rubber washers (and metal washers on top) to
seal the holes in the bottom of the cistern. These leaked massively. So
I added thin plastic washers between the pan and cistern.

Can't see that those plastic washers would help. The conical washers
seal by being forced into the holes in the base of the cistern.

I have undertightened, appropriately tightened and overtightened the
bolts. One is fine but the other still leaks whatever I do.

It could be the hole is so misshapen that the conical washer just won't
deform enough to seal in which case your supplier should replace the
cistern with one that does work.

What is the best way of sealing this connection? Fibre washers,
sealant, different conical washers (I have tried white stiffer ones
already) or what?

Sealant might work but if the cistern is defective it would be best to
exchange that and get an easy seal.

Several years ago I bought a new bathroom suite from Focus with such a
toilet but neglected to install it. I actually got round to fitting the
pan to the stack this very week but I have yet to plumb in the water
supply so I don't know if mine is going to leak. I have another toilet
so there is no pressure to complete.

--
Roger Chapman