280-20-70 R.I. Code R. § 32.7
In those cases where the taxpayer is unable to furnish the evidence required and outlined to support a claim for exemption at the time he or she purchases items of tangible personal property for use in a treatment facility, the taxpayer should pay the tax and thereafter, when able to properly support the claim for exemption, he or she should file a claim for refund. Such claim must indicate the items purchased, the date purchased and from whom purchased, the date installed in the facility, a statement that such items are and will continue to remain in use in such facility, satisfactory evidence that the sales or use tax on such items have been paid, the date of such payment and to whom paid, and certification by the Department of Environmental Management as indicated in in § 32.1 of this Part. All refund claims must be submitted no later than three (3) years from the fifteenth day after the close of the month for which the overpayment was made, or with respect to a determination, within six (6) months from the date of overpayment, whichever period expires later.
280 R.I. Code R. § 280-RICR-20-70-32.7