Discovering issues on a wet system that sat drained for some time can be "interesting"
B?G flow checks tend to stick in the last position and that would/should have been closed
if its stuck open - you may need more than a gentle tap to swing it to seat again - It may need to be back flushed - it may need to be taken apart
I have had issues with gravity flow just being too strong and weight needed to be added - This can be done by wrapping solder around the top of the check weight.
since we have no history of the system performance
the only correct answer is
check this link - about page 3http://documentlibrary.xylemappliedwate ... 51842E.pdf