Finding Boat Leaks

I think this issue has been addressed before but I can't find the thread, so I am starting a new one. 

I had my boat in the water for 3 days last week.  After it was on the trailer, I pulled the drain plug and a whole lot of water came out.  Any suggestions where to start looking?

Thanks guys.

Years back on 17ft alum deep v I owned. Had water coming in.  Put plugs on all the hose outlets and put back in the water. No leaks. 

Had a loose fitting on front livewell at the tank. 

Rivets were fine. 

Before you flood your boat, check to make sure the plug itself isn't bad or wasn't sealed up properly. Unless you did that already. Then flood away. 

Plug the livewell drain(s) on the outside of the boat and fill the livewell(s) with water. If you have a remote drain valve make sure it's in the open position, if not make sure the in-livewell plug is removed. If you have two livewells with independent drains be sure to fill and test each one independently to help isolate any possible leak.  

It is an Alumacraft Escape.  All the plumbing is under the floorboards.

I thought there were other posts, but I am not the only one who can't find them.

Mine came from the drain plug base

It was never stated if boat is fiberglass or aluminum? Or wood? 

What kind of boat is it? I'd eliminate leaking livewell hoses, valves, and pumps before moving onto finding a bad rivet.

Also try adding food coloring to the water... My hull is white I used red but still took me a long to find two holes...I also put in afloat switch on my bridge pump..

A seam or rivet is the mostly likely culprit.  I also had a boat leak from around the screws for the transducer, also had a livewell pump that went bad and leaked like crazy.  

Yes it appears All of the leaky boat threads and how to fix rivets have disappeared

I would suggest that you park your trailer on a nice level spot and fill the hull with some water and look for some leaks coming from the rivets or seems