I have to replace the o ring on the valve/tank of my sand filter. The plumbing going in and out is fixed so in order to raise the valve off the tank to get to the o ring I would have to cut the pvc pipes. My question is...is it ok to us pvc screw on unions in the plumbing or is it better to use connectors and re-glue. The former would make it easier to work on the filter as it ages but it also adds more points of failure to the plumbing system. I have a 25,000 SWG inground pool. The pumps and filters are in a room below the pool level.