When I did mine with a homemade manometer, I found that I needed to be careful of the connections where the hose hooked onto the nipples. I used vinyl hose, which loosens up when it gets hot. Some small spring-style hose clamps helped maintain a good seal. Also, not sure if it was mentioned elsewhere in this string, but it's a good idea to balance, then swap the hoses and re-check. If you've got a problem, such as a bad seal with one of the hoses, this will help reveal it (you'll balance it one way, but when you swap them, it will be out of balance).