For sealing threaded fittings on RV freshwater tanks, both Teflon tape and pipe thread sealant can be used; however, a high-quality pipe thread sealant rated for potable water is generally preferred as it offers a more reliable and durable seal under water pressure and vibration. When reinstalling the 3/8" barbed fitting, it should be threaded in securely until snug but should not be overtightened or bottomed out against the tank. Tighten just enough to compress the sealant without stressing or cracking the plastic or threads.