Silver knob on back of 1993 sport nautique?

[sls]

My buddy just bought this 1993 Sport Nautique. What is the silver knob on the left side of the stern for/control?

[Quinner]

Tough to tell from the pic, Is that a fresh water flush connection? Or was it a trim ring for a shower head??

[swc5150]

I'd guess flush port?

[ScooterMcgavin]

It does look like a fresh water engine flush hose port that is missing the cap. My 89 sport had one but was on the side (factory location)