John wrote:

Relation has a cistern that has a hairline crack (due to forcing in an
oversized flushing handle) - it is leaking slightly.

I was thinking of smearing silicon sealant over the inside. Any better
suggestions?

(I realise it really needs replacing - but it is an obsolete colour -
brown!!!!!!)

Ah. Dry out and use Epoxy resin - 5 or 30 minute will do, or even 2 hours.

In fact, thinking about it, use 24 hour stuff and then make it runny
with a hair dryer, and force in into the crack, wipe off surplus with
cellulose thinners, and then play the hairdryer over the crack until it
gels.

It will go off totally in an hour or two at sensible temperatures.

Epoxy is perfect for this - it will bond to the china, its runny enough
when warm to go in, but sticky enough as it cools to stay in, its sort
of brownish, and it fills gaps.

OTOH a layer of gaffer tape over the inside will also probably work - or
that sealing tape - sylastic? sylmastic? (sp?)