Weird fitting Moody 31 cockpit

[Jono as 2234]

I'm looking at a Moody to purchase. When the owner started the Volvo 28 hp, a small plastic fitting, resembling a small coffee pod began leaking water. When the cap was removed water flooded out and diminished the volume of water coming from the exhaust. It is situated on the cockpit side 300mm from the transom. This will be my 5 th yacht and never seen anything liked this before. Wtf is it
Thanks
Jon

[Calif.Ted]

Possibly a vented loop or anti-siphon device on the raw water intake.