Dice, don't leave any drains open. You are just venting the RV park sewer system thru your rig. Best not do that and wait until tanks are at least 2/3 - '3/4 full. You will get more of the soap scum, hair, etc out of the tanks and not gave any sewer bugs crawling back up into your grey ranks and beyond, such as into the sinks or shower. Wait until that happens, you will not be a "Happy Camper" when it does.
Brenda and John
'14 Ram 3500 MCSB 6.7L HO PullRite 16K S/G, Grey Columbus 320RS Camped '14 - 146 days/'15 - 196 days
USN-EOD(Ret), Master Chief, 30 yrs,
Master Blaster of the Navy