"HELP" line products from Dorman has two of those spherical vacuum reservoirs. One has its own built in check valve and has two hose connections. The other works with an external check valve and only one connection. With a little rearranging, you can use either. I like to use the one-connection one with a separate check valve. Last one I did, the Reservoir ended up in an awkward place, so I wanted the check valve out where I could get at it for troubleshooting. We had a failure, and I felt smart when it turned out to be check valve and it was right out there easy to change.
