rv2go wrote:
It's a foam rubber seal. Looks like this.
Most all camping stores will have it. Some Walmarts have RV supplies.
It has been my experience, that if a CG requires it, they have them for sale.
and fwiw it's been my experience that as long as you don't just dangle the end of the sewer hose into the hole you won't be bothered. we don't have a 'sewer donut' but we do make sure we have a sealed connection using the item below. in 28-seasons we've not been asked to use the donut. as long as you use something designed for the purpose you should be OK.
you can also minimize leaking odors throughout the CG by leaving your tank valves closed until ready to dump.