Gemara

(Rav Ashi): An utterly idle man (he does not work or learn) must pay a share of taxes imposed on the city (even though he earns no money in the city);

This is only if the king's tax collectors asked him to pay, and people of the city saved him. If he was saved through Andiski, Hash-m exempted him!

143a: Rav Yitzchak bar Yosef taught that once, the king demanded that the rich people and the (less rich) nobles buy a crown for him. Rebbi ruled that the rich pay half, and the nobles pay half.

Initially, the king wrote only that the rich must pay. The nobles used to help a small amount. When the king found out, he included the nobles to (increase the demand and) teach that each group pays half.

Bava Kama 116b (Beraisa): If a troop despoiled a caravan, and a member of the caravan saved some of what the troop took, everyone gets back his own things. If he told them that he saves for himself, he keeps it all.

Question: If others can also save, why does his declaration help?

Answer (Rami bar Chama): The case is, they were partners. In such a case, a partner can divide the property by himself. If he did not say that he saves for himself, they are still partners.

Rishonim

The Rif and Rosh (3:66) bring the Gemara on 55a.

Nimukei Yosef (DH Omar ha'Mechaber): The Gemara (8a) said that one who has lived in the city for 12 months must help pay for planks (used to support the wall). The same applies to taxes and conscription. This is when there is no fixed amount, and perhaps he causes it to be bigger, for he adds to the population. Rav Hai Gaon says that Andiski is a stamp from the king that he is exempt from the tax. This is only if it was before the collector started demanding payment, or before an amount was fixed for the city. If an amount was already fixed for the city, he is not exempted.

Darchei Moshe (CM 163:10): The Mordechai (Bava Kama 180,177) says that the same applies to anyone pardoned, even if he is not idle. R. Simchah obligates him only if he requested the officer to exempt him. Maharam says that if the officer pardoned him after fixing a sum for the Tzibur, he is exempt, but not if he pardoned him before fixing a sum for the Tzibur, for then the officer will make the Tzibur pay more to compensate. However, if the officer said on his own that Ploni will not pay, he is exempt even if they used to give together. Likewise, he can say that they will give equally. This is before the Tzibur settled with the officer. Once they settled, he cannot be lenient on one and stringent on another. Dina d'Malchusa Dina does not apply to this. However, perhaps even before settling, an officer, or even the king cannot be more lenient on one than another, for the Tzibur are partners regarding taxes.

Rosh (Bava Kama 10:25): A Tosefta teaches that if tax collectors pardoned partners, they share the savings. If the tax collectors said that this is due to Ploni, he was pardoned. R. Simchah asked that the Reisha is obvious! He answered that it teaches that if one partner requested pardon, the pardon is for both of them, as if he was his partner's Shali'ach. The Seifa says that if they said that this is due to Ploni, i.e. they exempted him without any request, he was pardoned. One could say that in the Reisha he requested pardon, and the pardon was Stam. When they specified that the pardon was for Ploni, it is only for him. However, if so the Reisha is not a Chidush. Surely, Stam pardon is for the partnership!

Mordechai (Bava Kama 177): Even if one partner requested pardon, the pardon is for both of them, for a partner cannot divide without his partner's consent, and one normally toils to help his partner. If they said by themselves that they pardon due to Ploni, he alone was pardoned. Based on this, R. Simchah ruled that if Reuven requested the officer to pardon him (even) after the officer fixed an amount for the Tzibur, Reuven must pay his share with the Tzibur. He wrote 'my uncle R. Klonimus used to ask pardon from the officer after he settled with Tzibur, and he would pay with the Tzibur. We thought that this was Midas Chasidus. Now I see that letter of the law requires it. Rabbeinu Meir rejected this (like the Rosh brought above). Therefore, if the Tzibur already settled with the officer, and then one requested pardon, he saved for himself. If this was before the Tzibur settled with the officer, he must pay, like we say about a troop that ravaged a caravan. If one saved, he saved for everyone. Whenever others can save, even if he said that he saves for himself, he saved for everyone. We follow the clear assessment that when the officer exempts one, he will collect more from the others. However, if the officer said by himself before settling that Ploni will be exempt, and David and Levi will be liable, Ploni is exempt, even if they used to give together. In Bava Basra 143a, even though the rich used to give more, when the king decreed that the others pay half, they do like the king says. An officer can exempt one and make another pay more before settled with Tzibur. Afterwards, he cannot, for they are partners, and they share the burden like they normally do. This is unlike Bava Basra 143a, for there they were not partners. The king obligated only the rich, and the others voluntarily gave a little.

Yam Shel Shlomo (Bava Kama 10:45): The Rosh said that it is no Chidush that if Ploni requested pardon, and the pardon was Stam, he pays with the others. I say that one might have thought that since he alone appeased, presumably the officer pardoned him! However, I disagree with Rabbeinu Meir's conclusion about a tax that they used to give together. His initial proof from 143a is valid. It makes no difference whether or not initially they were obligated to pay. There also, they used to give according to their money (the richer gave more)! He said that a partner cannot divide without his partner's consent. If needed to avoid a loss, he can! Also, he does not divide. The king does, and Dina d'Malchusa Dina! This is not theft, for they did not yet settle the amount.

Gra (CM 163:89): Dina d'Malchusa (laws of the kingdom that help the kingdom), is Dina, not Dina d'Malka (whatever the king decides - Ran (Gitin 4a DH Omar, v'Ibo'is).

Poskim

Shulchan Aruch (CM 163:6): If an idle man (Ploni) does no business in the city, and people of the city appeased for him, e.g. a tax collector came to collect the quota from (each of) them according to his estimation of their abilities, and they told him that Ploni cannot pay, and he exempted Ploni and imposed Ploni's quota on them, Ploni owes them. However, if he exempted Ploni by himself, even if he imposed Ploni's quota on them, Ploni is exempt.

Beis Yosef (DH v'Adam): The Rashbam explains like this. He is exempt when the collector overlooked him or did not bother to ask from him because he knew that Ploni is idle, and presumably he has no money.

Rema: An idle man is liable only if he lives in the city, but not if he just happened to come here, since he does not profit here. This is if they exempted him before fixing the tax. If they fixed the tax and afterwards exempted an idle man, he must pay his share. If the officer pardoned David from his share of the tax, if David requested this, he must pay his share to the Tzibur.

SMA (36): This is even if they do not collect from the Tzibur what David should have paid. This is because one is no different from his partners, and the entire Tzibur are partners in taxes.

SMA (37): He pays what he would have paid had he not been pardoned. The Tzibur spends it on the tax or other public needs, and he will benefit from it. This is the Mordechai's intent.

Rema: If the officer pardoned David on his own, this is David's gain. Some say that before settling with the officer, the officer has no power to exempt or be lenient on one of them and impose more on the others or separate them. After settling with the officer, if he pardoned one of them even through his request, this is his gain and he need not pay the Tzibur.

SMA (37): The latter opinion holds that if he pardons David after settling with the Tzibur, he will deduct this from the city's obligation. If he pardons David's share before settling, he will impose David's share on the others. The opposite applies to an idle man (Ploni). If he pardons Ploni after settling, he will not deduct this from the city's obligation, for he never intended that Ploni pay, for he is idle, therefore, Ploni is liable. If he pardons Ploni share before settling, Shamayim exempted Ploni.

Rebuttal (Taz): Before settling, if the king pardoned or forgot Ploni, he is exempt. This is like the Maharam's first version, that if the officer explicitly exempted Ploni before fixing the tax, without Ploni's request, Ploni is exempt. This version is primary. We cannot resolve this with the Mechaber. Before settling we do not distinguish an idle man from anyone else!

Shach (16): The Rema means that the officer has no power to exempt one who requests pardon. He can exempt one on his own, like the Mordechai says in the name of Maharam.

Shach (17): After settling, he can pardon one and that person will gain only if his exemption is not added to the Tzibur's obligation.