Hmm, I'm not sure. A drain to the outside is against the law except if its tied into your house sewer; so a single pit is used that would just get pumped out. I'm trying to find a solution to not have to pump it out. If I have a removable bucket of some sort in the floor, this would be easier than putting a pump in and stringing hose every time.
This would only be an issue in the winter. All the snow that melts off the vehicles is what this would be used for