How To Fix a Leaking PVC Union 

From www.swimmingpo... this video talks about a common leak source with PVC valves and union connections. If you have a black rubber O-ring or gasket inside of your PVC union then you might try to remove the O-ring and apply a silicone based lubricant to it. Leaks can develop over time as the gasket becomes dry (or misshapen / flattened) and the lubricant can help you to achieve a leak free seal. If the gasket is leaving black stains on your hands when you handle it then this indicates that the gasket or O-ring has reached the end if it's service life and you should consider replacing it.
Use an oil filter wrench to help you open tight / stuck PVC unions. • How To Open Tight PVC ...
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