The 23 has no inner hull - it is just one layer. If the hose from the cockpit floor drain has been disconnected, then (obviously!) don't launch it, and look in this forum for suggestions on the proper replacement hose (if you need one) and use two hose clamps each end. My guess is that the interior flooded because rain water drained through the cockpit floor drain directly into the bilge, rather than through the disconnected hose and out the transom. It could also have filled the cockpit through the access port by the gas tank storage, or of course via the companionway, the from anchor locker or even leaky chainplates or other deck fittings.
If you have not bought it yet, get rid of the water and carefully look at all the interior ply bulkheads. You'll have to crawl in the bilge, and also check in the storage lockers under the seats, and remove the floorboards. Pay particular attention to the afmost starboard locker, as it will probably be flooded, and if water has been in there a while, the ply may have disintegrated. If enough bulkhead wood is rotted, I'd pass on this boat, unless you want an awful lot of work. Mine had interior flooding through the gas tank port from the cockpit, which I didn't realize until after I bought it, but the damage to the wood was manageable - I basically just dried it out and removed the few outer peeled layers. Eventually I may apply some epoxy on top. On the hard, the drain in the cockpit very quickly gets blocked from leaves and doesn't drain at all - watch that if you buy it.
Peter