Hi, I'm very confused, my toilet has never missed a beat and has always worked fine, until last night. When I flush the water is now sucked out under vacuum I suppose, to the very bottom of the u bend, leaving the basin 50% exposed. Nothing has changed and no alterations have been made to the plumbing in the house. The toilet waste goes straight through the wall, into an external vertical stack then down into the drain (the drain is spotless and unblocked) the only other pipe into the stack is the washing machine waste pipe, the machine is in the kitchen, the washing machine waste pipe is cale tied into. An internal pipe, internal u bend, through the wall and then drops at about 35 degrees and pins the stack. I can't see if the top of the stack has a vent, I don't have a ladder tall enough? Any ideas.