They are lightly pressed into a rubber seal. I have had on some of our Newmar's have the plumping pipes have a loss fit or going in at a angel and not have a tight seal. Remember to use a lot of water when rinse both black and gray tanks. Should have a clear section in your drain line to make sure there isn't any other then clear water coming out of the tank. Sometimes we do 3 black tank rinses.
Tom/Teri 16031 NKK 117995 FMCA
18 London Aire 4531 Spartan K-3 605
97-04 LA 04-18 Essex 2018 London Aire