RV sewer lines are typically attached using a plastic or solvent weld which can't be separated and the only option is to cut off the entire section that has it and replace what's then missing. There won't be a way to separate the white sealant you have now so you'd be best off just cutting it all off.
For ABS solvent then we have the part # A05-0303. I attached a link to a page that has our sewer lines and adapters for more info as well. view full answer...