I cannot help with specifics because I have an Aria, but you are correct that the fabric should enclose the drain pipe to sort of close off the opening to the outside when the slide is extended.
If yours is like mine, there are hook and loop (Velcro) strips along the edges of the fabric and one section of fabric goes above the drain pipe and the other goes below. The two sections are secured to each other with the hook and loop strips. The drain pipe needs to be free to move within the fabric as the slide is extended and retracted.
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