Dealing with the black water tank has an ewww factor right off the scale for most folks, and for others it doesn't seem to bother them in all. I've done it so many years now that I've become used to it, but it's still not something I look forward to.
Whether you're in an RV Park or Boondocking you are supposed to wait until the black water tank is at least three quarters full before you dump it. That's to ensure there is enough water flow to wash everything out of the tank. Sometimes waiting till it's almost full is not possible because you might need to move and you don't want to leave with a tank that's half full. I've had to do that myself and I've never had any problems. But one thing you never want to do is hook up your drain line in an RV Park and then leave your blackwater valve open. What will happen is the liquids will drain off and the solids will stay in the tank and since they're not sitting in liquid everything will dry out and be extremely difficult to get out of the tank sometimes requiring professional help to do so. Here is what you're supposed to do. When your black water tank is empty put 4 or 5 gallons of water in the tank, use the tank until it's about three quarters full, then dump the tank. Doing that will alleviate most of the problems that people have with their black water tank.
Most people have some way of rinsing out the tank after they dump it. And that's a good thing to do if you can, but I've talked to people that have told me they have never rinsed out there Blackwater tank and have never had a problem. I rinse mine out every once in a while and I've never had a problem.
If you want to start an argument while at an RV Park or Boondocking, just start talking about RV toilet paper, and chemicals to put into your black water tank, and you will find almost everyone has a different answer to those problems. So instead of starting that same argument here I will simply tell you what I've done for the last 25 years. For toilet paper I use most anything that's cheap and says septic tanks safe on the wrapper. Dedicated RV toilet paper is expensive, and I've seen test showing that it didn't break down any quicker than ordinary toilet paper. So I buy whatever's cheap at Walmart and in 25 years of doing that I have never had a problem with the black water tank in any RV I've owned.
Now as for the various blackwater tank chemicals, I have over the years tried various ones and cannot honestly say that any one of them worked any better than nothing at all. the first couple of months when I went full-time I didn't put any chemicals at all in my blackwater tank, and that's normally what I had been doing. But I figured that since I was going to be Boondocking for a month or more maybe I should put something in the tank especially in a hot place like the Arizona desert. So I bought something called Tank Techs RX. This stuff is supposed to contain, not just microbes, but powerful microbes, and other things thats supposed to be good for your black water tank. I've been using this for about two months now and so far I haven't seen much if any difference in the blackwater tank. And I think the reason is because I wasn't really having a problem before so there wasn't much for it to fix.
Finding a place to dump your gray and black water tanks is a big part of Boondocking. Just like trying to fill up your freshwater tank, dumping your gray and blackwater tanks can be free and easy or difficult and expensive. And that all depends on where you are and how many other RVers are trying to do the samething. There are various websites that have lists of places you can dump in your area. But often there out of date and still list places that are closed. My normal way of finding a dumpsite is to talk to the boondockers around me. They will often have the most reliable and current information, because dumping is something we all have to do on a regular basis.
There are some free places to dump your tanks but they're getting more and more hard-to-find. A lot of places now charge a fee and anywhere between 5 and $10 is normal. I've even run into some places that charged $20 to dump, of course I keep moving on down the road when I hear that.
A word to the wise, don't cheap out on your sewer hose. Do yourself a favor and buy a good quality sewer hose. It will last longer, it will leak less, and will probably even take up less space where you store it than one of the cheap blue hoses. And while you're buying a high-quality hose buy a clear fitting that goes between the hose and the RV so you can see whats coming out, and more importantly when it's finished coming out so you don't block up the dump site trying to guess when your tank is empty.
There's actually a lot more things I could say about the Blackwater tank but this post is getting kind of long and I don't want to bore my readers any more than necessary. The last consumable I write about will be electricity, and I saved it for last because it's my favorite.