Camco
RV or marine antifreeze is used when winterizing plumbing so water left in the lines is less likely to freeze and damage them. If your RV stays in freezing-free weather, you may not need it.
RV owners who winterize or store in cold climates.
Camco RV Brass Blow Out Plug - Essential RV Winterizing Tool - Heavy-Duty Brass Construction - Helps Clear Your Water Lines During RV Winterization and Dewinterization (36153) (ASIN B0006IX68O). Amazon's page has the current price, specs and reviews.
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Check current Amazon listing (ASIN B0006IX68O).
Fine print: The Dude has not personally tested this product. The details on this page come from the Amazon listing and can change; check the listing for the current specs, price and availability.