According to the Tanchuma (Parshas Nasso 29) It is
forbidden to make any use of the oil that is left over from the Chanukah
candles because it was designated for a mitzvah. Therefore, it should be
discarded by burning it up separately. A person shouldn’t say I am not going
to fulfill the mitzvos of the Elders since they are not from the Torah. G-d
says to him, My son, you are not permitted to say that. You should do
everything they ordained…for I agree to all their decisions.
It is forbidden to derive benefit from form the oil or the
wicks of the Chanukah candles even if they went out only after they had burned
the full time required to fulfill the mitzvah. This prohibition applies not
only the one candle that is required to fulfill the mitzvah, but also the
additional candles we light as hidur mitzvah, for they, too, have been
set apart to be used in the performance of the mitzvah.
Oil that remains in the bottle is not prohibited even
though the oil that was used in the menorah was taken from it.
Oil that is left over from the Chanukah candles should not
be saved to be used the following year. Since it is forbidden to derive
benefit from it, we are afraid that it will be used, if only accidentally.
Even if it is stored in a container which is repellent, it may not be saved.
Using something to do a mitzvah is not considered getting
benefit from it, but we light Shabbos candles in order to benefit from them.
Therefore, It is forbidden to use the oil that is left over from the Chanukah
candles for Shabbos candles. For the same reason, it is forbidden to use oil
that is Orlah for Shabbos candles.
If oil that is left over from the Chanukah candles mixes
with other oil, it may be used if there are sixty parts of the permitted oil
against one part of the forbidden oil. If there are fewer than sixty parts of
permitted oil, there is disagreement among the poskim whether it is permitted
to add permitted oil to the mixture. In practice, the later poskim are machmir.
It is important, when burning the oil and wicks that are
left over from the Chanukah candles not to touch them with a knife or fork,
for they will absorb the prohibited oil. It that happens, they can be kashered
by hagala. Libun is not necessary.
Oil that remains from Shabbos candles after they have gone
out may be used for any purpose. When oil remains from a yarzeit candle
after it has gone out we are careful not to use it. According to the book of
the customs of the Jewish community in Worms by Rav Yuzpa Shamash part two,
page 249, a wax candle that has once been lit in a synagogue may be lit only
in a synagogue, for we enhance but do not diminish kedushah. The remains of a
yahrzeit candle may not be used for the same reason.