Delmar changed its name three times before the mail caught up
Delmar started out as Adamsville, named for Nathaniel Adams, who built a hotel there in 1836 and became the settlement's first postmaster when its post office opened in 1840. Mail kept getting confused with Adams, New York, so the post office became Adams Station -- until the Albany and Susquehanna Railroad's own station name won out, and a resident petition made it official as Delmar in 1892.
Layered plumbing from three eras of Delmar construction
That renaming history maps roughly onto three waves of construction: an 1830s-1840s Adamsville-era core, growth tied to the Albany and Susquehanna line through the mid-1800s, and everything built after the 1892 Delmar rename. A supply or drain job near the hamlet's original center should expect older pipe runs that a newer Delmar-era addition down the street won't have.
Plumbing work common in Delmar
What to have ready
If you know roughly which construction era your section of Delmar falls into, mention it -- it changes what kind of pipe a plumber expects to find. Otherwise just note when the issue started and which fixtures are affected.