What is a pool plunger valve?
Beside this, how does a plunger valve work?
It is designed to let air into the suction side of the pump (making it loose prime) if the intake gets restricted. This is a safety feature to prevent entrapment. They also let the hoses hang straight down. There is a close up picture of the "B-adapter" and a plunger valve in this thread.
Herein, why is my Intex pool pump leaking?
Water Leaks An Intex sand filer pump's pre-filter cover may sometimes experience a leak. In most cases, this is due to the O-ring inside the filter pump being jammed in place too tightly. Applying a thin layer of petroleum jelly over the O-ring helps it move more easily and prevents water from backing up inside.
Water would come out of the backwash line if the spider gasket in the diverter is bad. Although you have a new valve, the spider gasket could already be pinched or damaged. Remember to always turn the valve in the same direction. Going back and forth can cause the gasket to get pinched and then you'll have leaks.