the check valve needs to be rotated so that it is level once the ck valve is level. it will keep the water from leaving the tank IF IT is installed correctly with the arrow pointed in the direction of flow and level not real sure what else you are trying to do, but the ck is the reason water is coming back others may have different ideas

picture of the new installed ck valve. i see a climpse of it. and I THINK you have a swing check installed as a spring ck. swing ck can only be installed on a plumb/level horizonital line. it ck gate, works by gravity , it swings spring ck, can be installed both vertical/horiz. it uses a spring

Quote: Originally Posted by frodo picture of the new installed ck valve. i see a climpse of it. and I THINK you have a swing check installed as a spring ck. swing ck can only be installed on a plumb/level horizonital line. it ck gate, works by gravity , it swings spring ck, can be installed both vertical/horiz. it uses a spring yep, the plumber has made that mistake,but the issue in the problem is not caused by this. As even if this check not works loft will be filled by both direction(from top & from bottom) Right? The issue is when I am not at home,when I come back I see the tank is drained,I have verified that level below apartment gets this returned water.(The high loop didn't worked out ) Also,I don't to wish to involve any type of check valve because of the corrosion issue due to hard water. How to make high loop outside work as i desired/thought.