Black Tank Flush. Is it totally isolated?

[Laidback1]

Folks, I used the instructions that several of you provided in my post a couple of days ago on how to flush the black tank. I kept the black tank dump valve open and just flushed until things ran clear. Took about 10 minutes which seemed a long time considering that this was just my second trip out on the new rig. Question: the sewer connection at the camp site was 1 feet above ground and I do not have sewer pipe supporter so there was a pretty big rise that the flow had to go up from ground level to the the site connection opening.
I was parked close to the sewer connection so the sewer pipe “slinky” was compressed fairly short. I got doing a few other things and came back to realize that after a while there was not a lot of volume flow and the flush water was not pushing over the rise into the site dump and was just backing up in the sewer pipe and I’m sure some went back into the black tank. I checked inside and the tank indicator showed that the tank was nowhere near full and nothing backed up into the toilet. There is no way for this back flow to get into other parts of the water system is there? I wouldn’t see how but just want to make sure.....
Mark

[BabyBober]

Folks, I used the instructions that several of you provided in my post a couple of days ago on how to flush the black tank. I kept the black tank dump valve open and just flushed until things ran clear. Took about 10 minutes which seemed a long time considering that this was just my second trip out on the new rig. Question: the sewer connection at the camp site was 1 feet above ground and I do not have sewer pipe supporter so there was a pretty big rise that the flow had to go up from ground level to the the site connection opening.
I was parked close to the sewer connection so the sewer pipe “slinky” was compressed fairly short. I got doing a few other things and came back to realize that after a while there was not a lot of volume flow and the flush water was not pushing over the rise into the site dump and was just backing up in the sewer pipe and I’m sure some went back into the black tank. I checked inside and the tank indicator showed that the tank was nowhere near full and nothing backed up into the toilet. There is no way for this back flow to get into other parts of the water system is there? I wouldn’t see how but just want to make sure.....
Mark

Completely isolated within the camper. You ar safe there.

Jim

[Bob/OlallaWA]

I guess it is nice to have a black tank so clean you could camp in there but why? First time out again it will be dirty. If every camp site flushed two or three times the drain field would not be working all that well and what a waste of good fresh water. At what point is enough enough?

[bertschb]

I think the people who like to do a thorough job of flushing the black tank want to prevent solids from building up, prevent clogs and also to keep the tank gauges working.

[jim1521]

Well, I suppose if you had the black tank valve AND the grey tank valve both open at the same time there could possibly be a "backwash" possibility, but I don't know that for certain.

[bogen2]

Question: the sewer connection at the camp site was 1 feet above ground and I do not have sewer pipe supporter so there was a pretty big rise that the flow had to go up from ground level to the the site connection opening.

I usually just put something under the slinky to keep it all downhill. Anything at hand can work - leveling blocks, firewood, rocks etc.

Bob

[cmillsbl]

As long as the discharge connection at the camper is at a higher elevation than the rest of the sewer hose all the way to the campsite connection, I don't see how there could be any backwash into the camper. There could be standing black/gray water between the discharge connection and the next highest point in the sewer hose. Standard Operating Procedure should always be to close the black water dump valve before opening the gray water dump valve to avoid possible cross contamination.

I just bought three 6 foot red cedar planks (1 x 8) today that I will be using to create a raised constant slope from camper discharge point to campsite sewer connection. I'll place the sewer slinky on top of this and use the yellow lego type leveler blocks under the boards to get the slope I need to the sewer connection.

Our last campsite had a 3" sewer pipe connection with no internal threads and sat about 6" above ground. It was too small to use a spongy donut to hold my elbow in place, and too big to hold just the elbow in place. So now I have a 14" x 26" sand bag with smooth river rocks in it. I will be able to just lay it over the elbow to hold it in place in case I come across this situation in the future.

[Bob/OlallaWA]

I agree it is nice to get most of the stuff out of the tank, but how clean does it really need to be. I have been using black tanks in RV's since the mid 70's and have not had a problem with build-ups in the tanks. It has only been the last couple trailers that have even had a flush system. As long as you start with a few gallons of water in the tank and have around 3/4 full tank before dumping, and running the flusher a minute or two things should be fine. Go ahead and clean it out good before the end of season but I don't think it needs to be completely cleaned each time you dump. Next time you dump and things are not working right, thank the people who cleaned and cleaned and cleaned before packing up and leaving.

[Cate&Rob]

I usually just put something under the slinky to keep it all downhill. Anything at hand can work - leveling blocks, firewood, rocks etc.

Bob

I see this all the time at RV parks, but you really don't want your slinky to be a downhill slope all the way to the drain hole.

Lots of nasty things live in sewer systems from sewer gas to flies and bugs to crawling critters. There should always be a "P" trap in your slinky that stays full of water to seal your system from the park sewer system . . . just like every drain in your house has a P trap for this purpose. This is particularly important for those who leave their grey gate valves open at a FHU site (another practice that I don't agree with).

Just my 2 cents worth . . .

Rob

[Cate&Rob]

I guess it is nice to have a black tank so clean you could camp in there but why? First time out again it will be dirty. If every camp site flushed two or three times the drain field would not be working all that well and what a waste of good fresh water. At what point is enough enough?

Remember that there is about 1/2" of "stuff" in the bottom of every grey/black tank that cannot get over the lower flange of the gate valve. You can stir this up with the flusher, but there will always be liquid there that can't get out. The built in flush system is up high up on the tank wall at the opposite end from the gate valve. It washes down the walls, but doesn't really stir up whats on the floor of the tank. I have flushed with the built in system until the outflow was clear and then gone in with the hand help unit down the toilet and stirred up a lot more sediment.

Before winterizing, I crank the front of the trailer as high as I can with full landing gear extension on top of blocking. This will drain another couple of gallons out of the forward tanks and the reverse will do the same for the rearward tank. Obviously this is not something to be done at every tank draining.

Rob