Source: Nethack spoilers.
www.win.tue.nl/games/roguelike/nethack
In Nethack, one way to identify a ring is to drop it
on top of a sink and see what message you get. You then
have to look it up using the table included below.
That's the good news. The bad news is that
there is a 95% chance that the ring will fall
down the drain and (as far as I know) be
unrecoverable. Please /msg me if you know how to
prevent this or get the ring back.
Also, repeatedly kicking the sink will unleash
some black ooze which will kill you.
Here's the table:
Ring Message
meat ring Several flies buzz around the sink.
Works when blind.
adornment The faucets flash brightly for a moment.
If you are unblind and there are any items on the
hunger sink (except ball or chain) and they fail a
resistance roll, they disappear:
Suddenly, vanishes from the sink!
protection The sink glows silver/black for a moment.
depending on non-negative/negative enchantment.
prot from shape
changers The sink looks nothing like a fountain.
stealth The sink seems to blend into the floor for a
moment.
sustain ability The water flow seems fixed.
Works when blind.
warning The sink glows white for a moment.
aggravate monster Several flies buzz angrily around the sink.
Works when blind.
cold resistance The cold water faucet flashes brightly for a
moment.
The water flow seems greater/lesser now.
gain constitution depending on non-negative/negative enchantment.
Works when blind.
The water flow seems stronger/weaker now.
gain strength depending on non-negative/negative enchantment.
Works when blind.
The water flow hits/misses the drain. depending
increase accuracy on non-negative/negative enchantment.
Works when blind.
The water's force seems stronger/weaker now.
increase damage depending on non-negative/negative enchantment.
Works when blind.
invisibility You don't see anything happen to the sink.
poison resistance You smell rotten .
Works when blind.
see invisible You see some air in the sink.
shock resistance Static electricity surrounds the sink.
Works when blind.
fire resistance The hot water faucet flashes brightly for a
moment.
free action You see the ring slide right down the drain!
levitation The sink quivers upward for a moment.
Works when blind.
regeneration The sink looks as good as new.
You thought your ring got lost in the sink, but
searching there it is!
You never lose the ring.
Works when blind.
The ring is regurgitated!
slow digestion You never lose the ring.
Works when blind.
teleportation The sink momentarily vanishes.
conflict You hear loud noises coming from the drain.
Works when blind.
polymorph The sink momentarily looks like a fountain.
polymorph control The sink momentarily looks like a regularly
erupting geyser.
teleport control The sink looks like it is being beamed aboard
somewhere.
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Last changed: March 22, 2000
Nethack spoilers: rings / Boudewijn Waijers / kroisos@win.tue.nl
foofernarf adds, "If you drink from the sink repeatedly, you can find
a ring (or toxic wastes that make you polymorph, or random potions).
Also if you kick the sink enough it'll say 'The dishwasher returns!' and
an incubus or succubus will appear, depending on your gender."