I have 3 bathroom commodes. Two on the 2nd floor and one on the first floor.Every other day or so, the commode bowl on the 1st floor will almost empty itself on its own. Nothing has been changed in over 25 years and this has started only recently. Any idea's as to why this is happening and how to fix it ?
Jetty

Hey Jetty,
Your toilet bowl emptying is caused by suction pulling the water out of the trap in the bowl band the suction's caused but a clogged vent not venting the system behind a flush or a fixture when it discharges. The solution would be to snake the lavatory roof vent. Put out enough snake to reach the base and 20 feet more.
Good luck, Tom

Do this test: Have somebody to go upstairs. You stand downstairs by the toilet. Make sure the toilet has normal water level in it. Have the person upstairs to flush toilet. Observe water level in the downstairs toilet. See if it moves, shakes, or siphons in front of you. Get back to us...