RE: YOU KILLED, NOW WHAT?
Washing out the cavity can facilitate bacteria growth if the other requirements for bacteria growth are met. It must have food which is there, moisture (which is there, water just adds more), warmth, and time. However as long as the temperature is lowered and the deer is butchered within a reasonable about of time it will not matter. Just make sure to lower the temp, lower the better to stop the bacteria from multiplying. Case in point if you wash it out ice it or cool it down then it won’t matter if you wash it out or not.