The downstairs toilet has very little water in the bowl. When you flush it flushes ok and then fills up but then water drains away with almost no water left in bowl. Any ideas what causes this or how to resolve it?
The water level should remain at that of the U bend. If not, then perhaps you are suffering from a syphoning effect caused by inadequate ventilation of the stack. Is this a house, apt., etc.?
If the vent stack is high and out in the open and it's VERY windy the water in the bowl will move a bit. This will rock the water over the bend and make the water is the bowl seem lower than usual.
It should only happen at windy times though. Nothing to worry about if it's intermittent.