Your sinks are clogged
Recently, I had a couple tell me during checkout that both sinks in their room would not drain. I wondered why they did not tell anyone before checkout. I apologized and told them I would have maintenance check it out. I let my manager know, and he asked me to go to the room to see if the sinks were really clogged. Both sinks were full of water. I stuck my gloved hand in the kitchen sink and pulled out the sink stopper; the water instantly drained. I then went to the bathroom and discovered the stopper was in the closed position. I pulled up the stopper, and the sink instantly drained. I ran water in both sinks to make sure there was not a clog. It was just guests who did not know how sinks operate and did not want to investigate the issue.
TL;DR: Guests claimed their sinks were clogged, but it was user error.