I've read Elisa was completely nude in the cistern, no clothing, no socks, no shoes
I've also read LE/Fire Dept believe the clogging of the water lines were her clothes and it's possible they know this because some of her clothing may have been stuck in the drainage valve...
Which makes me believe the perp's likely an employee, since who would've thought of dropping her clothes into a chlorinated water tank --which would pretty much cleanse/bleach off DNA, prints, etc of the perp after she was killed?
I seriously think the average perp would'nt be aware of this oppotunity to hide the crime evidence in this manner...The perp has to be someone very aware of the hotel's facilities
You might have hit it right. Her sandals and heavier clothing might have been trapped at the drainage valve. The clothing would then act like a filter, stopping any decomposed material from going through. Meanwhile the water at the bottom turned black from the accumulation of decomposed stuffs. That would explain why residents saw black water only at the beginning when they turned on the faucet, but otherwise didn't find anything that unusual to raise their suspicion. (Of course, once they heard the news, all sorts of imagination would come in and their description of the water's taste might get exaggerated.)
But as another person has pointed out, how would it be possible for all her clothing to come loose on their own supposed if there was no foul play and assuming that she did not unclothe herself? Can the swirling in the tank be that strong?