I recently bought my boat from my uncle. I've taken it out twice or about three hours each time so far and when I pull the plug it drains for a good 2 minutes

I replaced the bilge that was not working and still can't figure it out. There are three holes in the back two white and one black. I assume the black is for the livewell dump and the other white is for the livewell intake. I only plug the one thats not hooked to any hoses. I've checked the hull and all the rivets and theres no cracks or holes. Please help
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1992 1706 Bluefin/Spectrum w/70h Force
Pulled by 02 Ford F-150 SuperCrew Lariet 4x4
*For sale* 81 12' Mirocraft w/trailer