To work optimally, there would have to be a directional cup on the hull bottom facing the stern to create a sucking venturi to pull water out of the hull and thru a down facing hole. Amd the plug wpuld be on the inside, where it someone mentioned wate pressure is working against you, at rest.
Lots of vintage tin and glass boats have this pod on the bottom of the hull.
It sticks down, and can be damaged or in the way on the trailer or beached....
Sticking down it also creates drag and turbulence below the hull.
Lost favor w manufacturers.
I had a 1960 Glaspar G3 for about 10min, and it had a long handled bilge plug apparatus (original to the boat, dealer added?) that was spring loaded to maintain pressure against the transom.
From the helm (its a short 13ft boat) you could turn 1/2way around and reach the handle. Push in and turn the handle from 3 oclock, down to 6 oclock and the bilge hole wss plugged. Push in and reverse, and the plug was out of the hole enough to let water drain out the back.
Neat feature and handy to have/use, but lots of moving parts compared to a flip or screw type plug and awkward for whoever was sitting behind the captain to have poking out beside (into?) their back... Ever now and then I see a similar setup for sale on ebay..