I do not use a resvoir but aways install a resin trap to protect the pump. Can be made from PVC pipe and fittings. I have found it very useful to install a plastic ball valve in the vacuum line just before entry into the bag. That way you can control how fast a vacuum is drawn and stop the process if needed. For instance, if the bag is drawing down and you notice a piece of foam core or fabric is a little bit out of position, you can shut the valve and reposition it. Once a hard vacuum is drawn it is impossible to adjust anything. And, without a valve, you would have to go secure the pump and disconnect supply piping.