How to remove black water clog

[LK23]

We live full-time in our 2017 DS 4369. Our black water tank is slow to drain. I have used a mirror to look at the waste valve with the tank emptied and all is OK that I can see.

We have a macerator toilet. Every time I dump I follow with a 40% fill of water and dump again. Then I run the black water flush about 20 seconds to add water to the bottom of the tank. I would think this is enough to keep the tank clean.

We also add Camco TST after each dump.

I don't know how, but I suspect I have a clog where the tank empties into the waste pipe.

Anyone experienced this?

How should I fix it? Chemicals?

I would appreciate your comments.

Rex

[Milford 47]

We have a macerator that drains into the grey and a regular toilet that goes into the black

The transfer line from the grey is 1.5 inches instead of 3 so it becomes an issue

Over the years if DW doesn't follow the proper fill procedure and let it time out we will get blockage on occasion

I use chemicals, no favorite, and try to remind about filling the bowl

[Old-Biscuit]

Old problem OR NEW?


When looking with camera do you have enough camera cable length to see tank outlet?


Sometimes the cut out disc falls inside the tank when installer is doing the vent/drain pipe/dump pipe installs and just leaves it.
Cutout disc can float around, stay away from outlet opening until one day it gets sucked into/up against outlet opening thereby blocking/restricting flow OUT when drain tank


With macerator TP/Poop clogging is less likely due to the stuff being in a slurry form.....unless you LEAVE black tank dump valve open when connected to sewer
Then that surry stuff can build up.




Could try one of those clear backflush adapters.....connect to dump line/hose and force water back up thru dump line to attempt clearing any obstruction

[LK23]

Thanks. I have the Valtera backwater flush connection on order with Amazon. In the meantime, is there a good enzyme chemical to break down the stuff that might be in the tank.

[Old-Biscuit]

Unique RV Digest It


Will break down/dissolve dog food in 2 hours


https://www.amazon.com/Unique-Digest.../dp/B07564FPHL

[FL420]

I bought one of those backflush adapters that O-B mentioned. Didn't work for me as my black tank drain pipe makes two 90° turns before it exits. It slowed the water down too much to clear the blockage.
I assembled my own clog blaster from parts on hand and hose and connections from the local hardware store. Worked great.[emoji106]

[LK23]

FLO420

Can you post a larger photo? What size plastic hose? And What spray nozzle is on the end?

Am I guessing correctly that once you spray water into the tank you have a mess of gunk that rushes out when you remove the black cap?

Rex

[JohnLoves2Sk]

Mix 1-2 bottles of liquid hand soap with a gallon of hot water and dump it in the tank, it will start breaking down stuff pretty quickly. Drive around the block a couple of times to help mix it up and possible dislodge the issue. After an hour or so attempt to dump.

If that doesn't work, get a clear discharge hose adapter elbow. Drill a hole in the side that will allow you to insert a section of cut-off garden hose.
*Mark the garden hose first, at 6" and 12" from the end*
Insert hose and run it up through the open valve until you feel the obstruction. Turn on the water. Ensure someone watches tank level ON THE GAUGES (NEVER OPEN THE TOILET WHILE DOING THIS)
Once the sewage starts to move, shut off the water, pull the hose out slowly, looking for those 12" and 6" markings. Don't pull it past the 6" mark until the tank is drained.
Good Luck!

[FL420]

Originally Posted by LK23

FLO420

Can you post a larger photo? What size plastic hose? And What spray nozzle is on the end?

Am I guessing correctly that once you spray water into the tank you have a mess of gunk that rushes out when you remove the black cap?

Rex

It blows up pretty well if you tap on it then zoom in by spreading it with two fingers, assuming you're using the app. Did you try that? If that doesn't work for you I will dig it out of the basement and try to get a closer pic for you.
The vinyl hose is 3/4" diameter which fits snugly enough to prevent leaks while allowing you to push it through the black cap to snake around the bends in the pipe to reach the blockage. A female barbed 3/4" garden hose thread is on one end of the hose while its male counterpart is on the other end. Attached to the male end is a brass hose end designed as a high pressure driveway sweeper.
On my coach I pushed the nozzle through the first 90° bend, past the open black tank valve, through the second 90° until it reached the blockage at the bottom of the tank. I then fastened the cap to the nubs on the drain to prevent any liquid from flooding out. After turning on the water it took just a few seconds to clear the blockage. After turning the water off I withdrew the hose until it was stopped against the black cap. I then closed the black tank valve, placed a bucket under the drain to catch the small amount of gunk trapped between the closed valve and the black cap and slowly unfastened the cap from the drain pipe.
After hooking up my drain hose as usual did the normal dump with no problems.

[Car1]

This is just a thought I have, which would eliminate one possibility and easy to do. Try having someone flush the toilet at the same time you are draining the tank. That would introduce air into the tank as does the vent. If the dumping process returns to normal or at least increases while the toilet is being flushed, that would indicate a blocked or malfunctioning vent. Something simple to try. It's unfortunate that when a tank is drilled more care is not used to remove plastic chips or large coupons during installation.

[Dav L]

If it continues to be a problem, last chance it to use a power washer with a "jetter" tip on the end. This, when inserted into the open drain valve, will pull itself into the tank and spray it clean. Deluxe is to modify one of the garden hose flusher adapters to allow for the pressure wash hose to be inserted alongside the garden hose so the tank can drain into a disposal tank with minimal blowback. If you can't reach the tank insides that way, you can also try from the toilet using a towel around the opening and with the tank drain opened to the disposal tank. That won't work for a macerator toilet though.

This is never a nice project, but it sure beats removing the tank.

[sawmillman]

Our black tank became completely plugged last year while out west. Used one of the clean out connectors pictured above. Took a few minutes but broke it loose. U can purchase at Wal-Mart

[rlott2k]

Fought this problem with a trailer years ago. Needed a plumber with a pressure washer hose to go up the black exit to break up a towel the previous owner flushed down.
Used a camera to confirm problem solved.
Was the only solution for my problem.

[FLJOE]

Rex, with both macerator toilets in your model I find it hard to believe there is a build up of anything, especially since you are rinsing after dumping your black tank.

As already stated I would suspect the cut out plug from tank install was allowed to drop into the tank and has now settled partially across the exit hole. Back flushing with an attachment could move it out of the way. Keep in mind that if you use one of the clear elbows with the garden hose attachments that was suggested you may have to deal with some unwanted black water coming back at you when removed it. I would get one with a built in gate valve if it were me.

Look up a Valterra F02-4350 Flush King

When we are in travel mode I always make sure my black and gray tanks are about 1/3 full. I add a couple pods of cleaner.