40 CFR § 267.203
What special requirements must I meet for incompatible wastes?
June 9, 2020
(a) You may not place incompatible wastes, or incompatible wastes and materials, in the same tank system, unless you comply with §267.17(b).
(b) You may not place hazardous waste in a tank system that has not been decontaminated and that previously held an incompatible waste or material, unless you comply with §267.17(b).