I would expect plumbing in something that was designed as a morgue, but they could also have used buckets and swabs.
Buckets and swabs, what ever next!
The plans show no plumbing, not even the entry point for the rising main into the structure. Even if you suggest after each supposed gassing a gaggle of scrubbers entered with buckets and rags, where did the water come from? Was there a human chain from a water vat stretching across the camp to the morgue? You are becoming entwined in the twisted logic of the lies that are peddled. It would take a great deal of time to empty the morgues, it would also take a great deal of time to wash them down and the clock's ticking all the time.
On the floor plans there are supposed gravity fed floor drains in the floor, not only are they situated right on top of the foundation that picks up the piers which would mean they would have to punch straight down through the strip foundation, (In wet ground raft foundations should be used to spread the load, not strip foundations which will take the loads to a small surface area and cause settlement) but what purpose would they serve? The base of the morgue was already at a depth that put it near the water table, so where would the water used to wash the morgues out run? The water problems under the morgues was so great it stopped the Germans building them completely sub-terrain, so if one punched a hole in the floor, water would enter into the room rather than flow away, especially during winter as the ground became saturated.
Maybe you could eleborate on your ideas a little, by all means use the plans as reference, after all that is the whole point of plans to use as reference for all the design details and layout isn't it?