My boat has always been bone dry inside, but after towing it in a couple of downpours, I noticed water under the step on the port side. Since the drain to the engine compartment is on the other side, figured it had to be a hatch, windshield etc. Turns out the plastic fitting for the anchor locker drain broke. A few small puddles were visible around the water tank, but when I snaked a wet/dry vac hose underneath the water tank compartment, I vacuumed out at least 3-4 gallons of water. I still don't know if there are other nooks an crannies where water could be trapped. Anyone know of a way to check? I recommend spot checking the drain since a lot of water must have entered before it became noticeable.

i just leave a little bleach in there and gave up

Mine had small hole in anchor locker and drain was plugged. Resealed and no more water.