WD 40 can leave a film which attracts dirt.
Lock-ese (guess on the name) is in a blue can at better hardware stores, it is a graphite spray, made for locks, goes in wet, then dries, leaves a dry slippery film that may not allow dirt to stick.
You can then get a can of air at computer supply stores, use it to blow out silt, then re-graphite as needed.
You may want to add an O ring to the male to make a dust resistant fit, then purchase a filler plug to use when not in use.
Tony & Lori
1989 Country Coach Savannah SE