Winterizing Question: Is My HWT Check Valve Leaking?

I put a new bypass on the water heater and it failed. Same setup with valve on cold and only check valve on hot. Wasted $18 and 2 gallons of antifreeze. Going to just buy more antifreeze and let it rip through city water inlet and pressurize the hot out to the shower. Via sump pump in a tub pressure

I have a dedicated sump pump for winterizing campers and boat motors.

I’ve had both the fresh water city check valve fail and the hoywater check valve fail- Took me two gallons to figure out I was filling up the hot water holding tank after I shut the by-pass off. The city water was kind of funny- I’d try to pressure up the system with the water pump and it would shoot out the side of the rv. Same trip the black water valve wouldn’t close.........

Thanks for the replies! I will go over the process again this weekend and check out the HWT drain. I actually did something stupid yesterday while pumping the pink stuff through. I forgot to shut off the outside shower faucet after blowing compress air through and went ahead pumping pink stuff. Before I knew what hit me, 2 jugs of them gone to the ground while I was inside the TT. I managed to use a spare jug to finish off all the other fixtures but it sure feels like there's some unfinished business.

Remove drain plug and see if you get water/air mixture blowing out

or your blowing way to much pressure and opening it up.

I would say yes you have a defective check valve.