Water shut of question

Hi all, stupid question but here goes. I've always filled my van up in the evening and turned of tap at night. It has a ball **** valve on the entrance to the tank in the van to stop over filling. My question. Is, if I left the tap running through the night by accident, and the valve shut of to the tank, would this in turn stop the water coming out the tap as it has no where to go or would it keep running through the waste pipe? It's a 4040 ro Di setup! 

Hope this makes sence

I must admit to forgetting to turn my tap off once or twice, in my experience it still flows from the waste but at a much reduced rate. I should say that I'm running into an IBC with no valve though.