How do you delete a custom object in ACS?

I'm looking for a way to delete a custom object in ACS, either via code or the web dashboard. For example, I create objects pinto and beetle that are cars, then delete pinto and beetle objects, the container object cars still remains as cars(0) in the dashboard. I would like to be able to delete it. I see no option, if I try to delete it via rest API:

httpWebRequest = (HttpWebRequest)WebRequest.Create("https://api.cloud.appcelerator.com/v1/objects/cars/admin_drop_collection.json?key=" + AppKey + "&session_id=" + SessionID);

I get a 400 bad request, even though I have other API functions working fine. I have also tried to figure out the ID of the remaining container and have not seen a way that works. Any suggestions or thoughts?