Not sure exactly what you're meaning by closed circuit, but the bags I own that are without an open end have an OPV, which can be removed for rinsing the inside of the bag if you're so inclined. I just use Tobin's hose-end tool to put some water in the bag, and then use the OPV to drain it out.
Agreed, not a problem at all. just pointing out to the OP that the "issue" of getting water in the bag is not going to be solved by getting a "closed" bag vs an "open" one.