Black plug on deck starboard stern corner

[jmccall]

I am trying to identify an unlabeled black hard plastic threaded plug (about 2 inch) in the deck of my starboard stern corner near the deck drain. I opened it and it smelled funky. Everything else on the deck is steel (I have two waste plugs also). Any ideas? I have a 1984 Defever Trawler 41T
John

 

[caltexflanc]

Picture or link to picture would help . Sounds like a PO addition. Did the surveyor mention anything or have you asked him?

 

[kchace]

Unfortunately, pretty much all fill or waste fittings are "about 2". Could be water, waste, gray water, fuel or even some completely bizarre PO installation. Is there any way to see whats connected on the underside?

Ken