Duplicants won't use Lavatory

I got the same problem

 

If the lavatory's error message is:

"In use" - you got contaminated water in the input pipe that broke your lavatory (needs lavatory rebuilding)

"empty pipe" - not getting input water

"not pumping" - your output pipe is full/oversaturated, need to rework it. (dont forget even if the pipe is empty, it can be still reserved by other output ports on the same line towards the contaminated water input port)

Exactly the same problem. Everything's connected and working just fine, but instead of using lavatories, they pee on the floor one after another like the lavatories weren't there.