Responsa על בבא בתרא 43:5

Q. A [moved out of T but nevertheless] lent money to his customers there. The community of T, therefore, forced him to pay taxes. He now claims that the community had no right to collect these taxes from him since he had made no new investments in T but merely had lent additional funds to his customers in order to be able to collect his old debts from them. The community representatives aver that A could have collected his debts without lending additional funds to his debtors.
A. If A could not have collected his debts unless he had lent additional funds to his debtors, he had a right to lend them such funds, and these transactions should have been tax-free. The members of the community, as interested parties, are not qualified to serve as witnesses in this matter. Therefore, either every member of the community must take an oath to support the claim of its representatives, or the community must permit A to take an oath in support of his contention. However, if the community can produce even a single, independent, witness — one who has no financial interest in this trial, or one from whom the community shall agree to take a certain specified amount as his share of the tax regardless of the outcome of this trial — in support of the claims of the representatives, or to the effect that A freed the community from the obligation of taking an oath, no oath will be required.
SOURCES: Cr. 156.

A, however, must pay his "tithe" to the community charity fund, from the profits he earned in T.