ATA (at least for Airframe Drainage) is 51-80. I had a few moments to drop downstairs and pop some pics.
Forward Relay Racks.
Radar R/T's and (just to the right in grey) Window Heat Controllers.
Main Batteries (aircraft right) and to the rear, the ATC Transponders and TCAS.
R/H Radio Rack with R/H Relay Rack just forward. I believe the relay cover just dumps into rack tray as I saw no hoses for the relay cover.
INS #2. The #1 & #3 INS are in the enclosure just above the #2. Those have their own water tray.
L/H Radio Rack Two drain hoses clearly visible.
Transformer Rectifiers (looking forward) and (I think) the Emergency Inverter just aft and lower.
What I "do" wonder about is if the passenger aircraft use all these trays. I couldn't imagine any massive amount of water coming in though the passenger doors. It should be minuscule compared to a cargo door.