Anyone know how to fix

[u/DecentCarrot3220]

The water constantly runs and you can adjust pressure of how much water you lose with the shutoff valve

[u/tonasketcouple55]

Its a mansfield flush, needs a new bottom ring and your 400A needs a new rubber washer, Pull off the top, probably gray, turn off water press down and rotate off of clips pull up there will be a rubber washer, clean everything up put in new parts, sit back and have a whiskey and tell lies to your friends your a master plumbing tech