That would be your flush valve in the tank
since check valve holds water in the line can a hand pump be installed between the check valve and water tank?
Back water valve
The purpose of the dishwasher drain check valve is to prevent dirty water from flowing back into the dishwasher after it has been drained. To check if the check valve is functioning properly, you can visually inspect it for any signs of damage or blockages, and also test it by running water through the drain to see if it flows in the correct direction without any leaks.
Check valves can go bad, however I can't imagine where you'd have a check valve in a normal hot water system.
Checks the flow of the water
The brine valve is located in the brine tank in the 3 inch tube. Systems with brass control valves prior to the year 2000 do not have a brine valve in the tank. the air check is performed by the tri guard. ( clear plastic thing with the ball in attached to the valve body)
First, check for any clogs in the cold water inlet hose and ensure it is not kinked or twisted. If the hose is clear, the issue may be with a faulty water inlet valve or sediment build-up in the valve. You can try cleaning the valve or replacing it if necessary.
The water valve may be open, but no water is coming out because there could be a blockage in the pipes, a malfunction in the valve, or a problem with the water supply. It is important to check for these issues to determine the cause of the problem.
To determine if the toilet water supply valve is leaking, check for any visible signs of water around the valve or listen for any hissing or dripping sounds.
The check valve is a directional valve. Hot water needs to be piped from the top of the tank to the fixture, because that is where the hottest water in the tank is. If a return line is tied into the bottom of the tank, a directional valve (check valve) should be installed between the heater and the pump. That's what they taught me don't know if it really matter upstream or down stream. If you don't have a check valve the water could flow through the return line to the fixture instead of through the supply pipe and the water at the fixture might not be hot enough.
A foot valve, in relation to a water well, is a check valve at he bottom of a well to keep the water from running back into the well from the pump when the pump is not running. If the check valve does not hold the water the pump will lose it's prime and will not pump water.