Years ago after the A300's major Mx visit, we started to get water dripping down from main deck into the E&E compartment and not in the pans where it should drain into. It would be raining down in the E&E compartment everywhere; the loading would stop so we could soak up the water from the main deck and E&E areas, which caused huge delays. Apparently at Heavy Check they were removing the flooring from position 1 on the main deck; furthermore, when they reinstalled the floors a different sealant was used causing a shit storm of delays during a rain event, while loading the main deck. Finally got it fixed. I'll try to get pics.
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.
Water would be dripping along the left walkway, over the IRUs, and center circuit breaker area. Major maintenance, like I said, removed the flooring at position 1 on main deck, and used a different sealant which caused the catastrophic water events. From what I heard, Airbus has never seen this happen to any other operator. The only reason we started to see water intrusion, was the pilots go down there for their preflight inspection.