Vacuum Toilet Why Does A Toilet Sometimes Flush Fine And Othertimes Need To Be Plunged?

Why does a toilet sometimes flush fine and othertimes need to be plunged? - vacuum toilet

My dress well, but often empty, and no overflow, unless it runs pretty fast.

Even in clear water poured into the bowl, not the toilet discharge does not, if the sink.

I do not think there is something wrong with the bathroom, and I wonder whether the pipeline could be the problem.

I have to discuss common problems, but can not explain why it overflows sometimes good, other times, and drains.
Is it possible that the drainage pipes could be close to the cause be? Could it be that it prevent the accumulation of empty washing?