I'm using a rubber stopper placed from the inside...
JC...
The drain cap on later model vans is NOT the same size as a garden hose
fitting. The sink is, but not the reservoir. I do not know of a source for a cap
that will fit. I have tried a variety of caps including plumbing hardware and
have yet to find something that matches. I will probably epoxy ours this spring,
as right now it has duct tape holding it together but it still drips.

Mark in AK