[Len2013]

I have a toilet in the basement, with a shower and sink also. S and S work fine but recently when I flushed the toilet the tank and the bowl fill and then the bowl drains away. There is a laundry tub next to this bathroom but I have never seen this before. Any suggestions on what I should try?

[smoothy]

Check your vents for a blockage... when they are blocked or restricted a vacuum forms behind the water being drained... and it sucks the toilet bowl dry being that is likely the point of least resistance.

[speedball1]

I have one that most repair plumbers miss.. Look down at the bottom of the bowl. If there is a small hole, then that is a jet that starts the syphon action. If it's clogged the water will just swirl around and slowly go down leaving solids behind. Take your finger,(UGH! ) and run it around the inside of the opening. Over the years minerals build up and cut down on the syphon (flush) action. If it is rough or you feel build up, take a table knife and put a bend in it to get around the curve in the bowl and chip and scrap it clear. Next take a coathanger and clear out the holes around the rim. They start the swirling action. And last, check the water level in the tank. It should be 1/2" below the top of the over flow tube. And speaking of the overflow tube, Make sure the small 1/8" tube from the ballcock to the white overflow tube is connected so it discharges in it and that it's flowing when the ballcock fills. This is what raises the water level in the bowl. For a good solid flush they all have to work together. Hope this helps. Good luck, Tom