Looks like a previous owner plumbed the icebox drain to the sink drain thru hull.
Does the green garden hose go to the sink?
With the boat out of the water, you need to install a seacock on the thru hull because it's below the waterline. Drain the icebox into the bilge or use a rubber stopper inside the box and pump/bail/sponge the melt water out.
The galvanized pipe t (with tapered pipe treads) has to go, not only will it not fit right but also the dissimilar metals plus water makes a battery and the less noble metal (galvanized steel) will get eaten away.
This is a big deal, you have no seacock/valve to close and protect your boat and if it lets go it can easily admit enough water to kill the battery powering the bilgepump and sink the boat.