When we are parked for any length of time, I always keep my waste tanks closed. On my unit we have three tanks, one for the kitchen, gray water and of course the ever so popular black water tank. The average RV normally has just two tanks, the gray and black.
Our stay here in Dickinson I noticed our neighbor's trailer. He has both drain valves open. I thought this was very strange. For the experienced Rver they would know to keep the black water tank closed. I had the opportunity to talk to him about his black water valve being open and he said that he has no problem with it and all that he does is flush the tank once in awhile.
To the novice Rver you may think "What's wrong with the black tank being open?" Lets start with the toilet and how it works. You do your business and push a lever. Done deal. This is correct but the novice is thinking it works just like at home. No it doesn't. Your Rv toilet is a gravity type toilet. This means that your business when flushed falls into the black tank via gravity. This is quite different from the house toilet which uses a gallon or so of water and pressure to send your business down to the sewer pipe.
Now think about it; You leave the black water tank open and when you flush, the solids will stay in the tank, start to build a pyrmid while the water will drain. Your black water tank acts like a mini septic system. The water being in the tank will help desolve the solids into liquid. To the new to Rvers out there "ALWAYS KEEP THE BLACK WATER VALVE CLOSED."
In some circles, you may research that it may be a good idea to keep the gray water tank open. Not a bad idea but it all depends what's going into that tank. If your kitchen sink drains into it then I would suggest keeping it closed. This may help with the small food particles that flow down the drain after doing the dishes.
Do you place toilet paper (TP) down the toilet? Some do and some don't. We do. We use White Cloud from Wal-Mart. We have used the TP for over two years now with no problems. It desolves in the water and very little clumping up to cause a plug.
If you feel comfortable using only the TP for Rv's then go for it I just don't like the price. You need to make sure that you use plenty of water when you flush, usually I count to five while flushing. So when do I "pull the valve to dump?"
I can use the panel and push a button that tells me when I am full or the best way to tell is when you flush the toilet and it gives you a little burp (air bubble). Now it's time to pull the valve and dump. My ten year old daughter even knows when daddy needs to pull the valve and dump. Well I hope that this gives you a little insight to your tanks underneith your trailer.
Until next time...................Be safe.