Use either of the two following methods:
(1) Use soap and water and not gasoline, as gasoline will injure the rubber. Lay out on a flat surface and scrub lightly with soap and water; then rinse with clear water. Do not wring. Put on a coat-hanger and hang out to dry.
(2) Pour some vinegar into a dish and dip a soft rag or sponge into it; then place the mackintosh on the table and rub the soiled parts lightly.