Plumbing question. How should my sink drain pipe be connected to my black water tank?

[VaDreamer]

My bathroom sink and black water tank vent pipe share a connection to my black water tank. Whenever the tank is full and the black water sloshes around, we notice a horrible smell in the coach and of course it’s leaking on the top of the tank. I thought there was a problem with one of the connections, so I have taken the shelves out of my sink vanity so I could see what was going on. I discovered the drain/vent pipe is not actually connected. The 1.5” vent/drain pipe is just sitting over the 2 or 2.5” threaded opening in the top of the tank. I can’t think it would be, but does anyone know if this is by design for some reason? I would think this pipe should actually to be connected to the top opening and that is what I plan to do. I need to know if I should glue the connections like everything else currently is or if I should connect it with one on those rubber sleeves. Gluing it will make it a ‘harder’ connection with no give and the sleeve will allow for some slight movement, without breaking the pipe. No give would mean the pipe could crack and the rubber sleeve could inadvertently become disconnected. Either would allow black water into the cabin area. At least the way it is now, the black water does not come into the cabin, only the smell does. Any thoughts or suggestions/recommendations?

[dpinvidic]

I would use a sleeve because the vent pipe should go through the roof, and is sealed at the roof. Don't break that seal.

Unless there are some elbows in the connection.

Someone likely forgot to make the connection at the factory.

Da

[slowmachine]

In another thread, you mention that this is a 1999 model. I think it is safe to assume that the pipe was connected to the tank at one time, rather than a factory assembly error. A rubber sleeve with hose clamps could be a good temporary fix. I would be trying to determine how the connection was broken in the first place. The worst-case scenario is probably that the black waste tank has come unsecured from its mounts and is moving around while you drive. It could be a lot messier than just a broken connection if you ignore it.


Mike
2000 HR Endeavor
Freightliner XC, CAT 3126B

[slowmachine]

Another thought... This could have been caused by someone carelessly applying pressure to the roof vent. Topside damage is also likely to cause water damage to the coach, so I wouldn't wait very long to examine it.


Mike
2000 HR Endeavor
Freightliner XC, CAT 3126B

[VaDreamer]

Unfortunately I cannot get to or even see much of the black water plumbing connections. It took several hours just to get to where I am, just to be able to look down through a 4" hole to see the tank opening. My goal at the moment is to get the issue fixed at least semi-permanently, use the coach for another year or 2 and then sell it and let the next owner deal with any new issues.

[Waiter21]

Rubber sleeve is probably easiest and offers flexibility of the joint.

[USA-RVNomads]

Usually a sink is connect to the gray tank. Only the toilet is connect to the black tank.

Have you tried adding any gray tank treatment...pouring it down the sinks and shower drains?

[Nana25K]

That horrible smell is coming from your gray tank not the black and is most likely from an accumulation of small food and grease particles
1. Under your sinks are small valves. At the age of your rig they are probable worn out. They unscrew. Go to any large hardware and buy new ones for a few dollars each
2. empty your gray tank, dump in a half a box of baking soda, a glug of vinegar and . Let it foam. Fo!low with very hot water. Now add a few Tablespoon of Dawn. Fill your gray tank by running water from your faucet Do this before departing on your next trip.
Upon arrival empty the gray. You will be amazed at the small junk, including hair that cones out

We do this treatment every 3 months No more nasty smell

[OLYLEN]

Many many bath sinks ARE connected to the black tank rather than the gray tank. OP has opened the area and confirmed this non connection problem. My MH has a sensual activation switch therefore all MH's have one, not ALL RV's have the same systems.

LEN

[Timon]

Sounds like the traps are not staying full.

That said, having the Kitchen sink plumbed to the Black tank is a good thing if you boondocking on BLM land. In some BLM locations your allowed to dump Gray water on the ground but only if you Kitchen sink and dishwasher do not go to the Gray tank since these dump food particles into the tank. Bathroom sinks, shower and cloths washer don't.

[VaDreamer]

Just an update on where I am and what I have done.

The bathroom sink is definitely draining into the black water tank. I'm sure it was done mostly for plumbing convenience, as the sink is directly over the black water tank. Not sure if the pipe was not connected from the factory or if the pipes was replaced and not reconnected. There was no good way to tell.

I cut the pipe with a hack saw and replaced the pipe section and elbow with an automotive radiator hose. I connected the hose to a threaded coupling and attached the coupling to the tank, so I now have a secure connection and all seems well. I plan to leave this as the permanent fix, since the radiator hose is more flexible than the ABS and should provide the same durability.

[Gary RVRoamer]

Sounds like a good solution to me.

[VaDreamer]

My radiator pipe solution is working like a champ, however now when I flush the toilet, I am getting smelly air backwash, as if the vent is stopped up.

Any ideas?

[ahicks]

My next step would find me up on the roof, checking to see if the vent is plugged and the cap is properly installed up there. On some of them, it might be possible to have the vent pipe that extends through the roof a little too far and become restricted by the cap when installed - not able to free flow as designed.

A bucket of water poured down the vent pipe would confirm it's open, not restricted in some unseen area.