Holding Black Water or Flowing Through

Adventurer Buck wrote:
Thanks for everyone's comments. I do hold waste and dump together (as suggested) and do not leave the line open (as asked). My reason for asking was that after dumping, I got an odor in the cabin. Another suggested that I not hold, and that's when I posted looking for consensus.

The problem turned out to be that when I dump, the suction from the grey water pulls the water from the traps which allows the grey tank's odor to escape through the drains up into the cabin. The solution: refill the traps with water after dumping.

Thanks again!!!

That shouldn't happen.........

Check under the sink cabinets for 'air admittance valves' just after the 'P' traps. They allow air into system when draining grey tanks so that the 'P' traps do NOT get sucked dry.

They are hand screwed into a short stub pipe.

Thanks for everyone's comments. I do hold waste and dump together (as suggested) and do not leave the line open (as asked). My reason for asking was that after dumping, I got an odor in the cabin. Another suggested that I not hold, and that's when I posted looking for consensus.

The problem turned out to be that when I dump, the suction from the grey water pulls the water from the traps which allows the grey tank's odor to escape through the drains up into the cabin. The solution: refill the traps with water after dumping.

Thanks again!!!

Dick_B wrote:
This is one of the very few topics on this Forum on which EVERYONE AGREES. Can't think of another one right off the top.

I don't think it's limited to this forum. :B

This is one of the very few topics on this Forum on which EVERYONE AGREES. Can't think of another one right off the top.

I use a bayonet valve between the normal exit and the sewage hose.

First, I dump the black normally (open the bayonet valve and the black tank valve.)

Then, I close the bayonet valve, open the gray water valve, let sit a few minutes. This will backflush the black tank. I then close the grey water valve, open the bayonet one, let drain. I might repeat this step once (which ends up cleaning the black water twice), then letting both tanks drain completely.

After that, close all valves, squirt some hand dish soap into the black tank, add a little bit of water, and it is ready.

I dump the black tank when it gets about 3/4 full. When about to leave a FHU site, I'll fill the black tank all the way up, and then dump it, so when I leave, all tanks are empty, except for a couple gallons in the black with soap. I have had the water evaporate, but the soap does remain and acts to keep the tank slippery to minimize any subsequent pyramids.

I don't leave the black tank drain open. I've seen too many nasties in sewer connectors including big slugs. Never have been able to fill the black tank. When we empty/flush the gray and black tanks it greatly speeds up the process if they are near full. Our black and gray tanks together hold 100 gallons. At 3 gph from campground it will take 30 minutes or so to fill them and then drain and then flush.
we leave the gray open when we have the washer running. Don't want to flood the coach like I nearly did. But generally we keep them closed. One thing I want and maybe can design is an alert to the gagues to let us know when, or if tanks get near full.

Welcome!

RV black and grey waste tanks are 'holding' tanks
As implied by their nomenclature......HOLD the stuff until tank is at least 3/4 full then dump.
If dump valve is open (particularly the black tank) the liquids will drain and the 'stuff' will just plop until it builds up into the dreaded poop pyramid.
Poop pyramids are tough to remove especially when they dry out and harden.
Not something you want to happen..........

The liquids help carry the stuff out of tank, Help break down the stuff. Helps keep the stuff from sticking. Liquids are good. More the better.

Dump black tank first......then rinse it. Close dump valve and add a couple of full toilet bowl flushes back into tank. Helps keep tank bottom wet so stuff doesn't stick.
Then dump grey tank to help rinse drain line/sewer hose.

Remember....liquids are your friend when it comes to waste 'holding' tanks.

I keep both valves closed until the tanks need dumping.

I have, by accident, left mine open.. ONCE.

Have you ever seen the add for Tank Additives that shows the very stinky RV.

Well, that was what I had when I left it open.

Closed the valve and things smelled sweeter in just a few minutes.

Keep it closed until ready to dump or you'll be back with a problem