Easy Backflushing to Clear a Clogged Black Tank

[djgodden]

I occasionally experience a blockage of my black tank when draining. We use "normal" house toilet paper for a myriad of reasons. Yes, I know it's not recommended. But I found a quick and easy way to clear a blocked line. I use the gray water tank, it should be full or nearly so to accomplish this.

I purchased an accessory gate valve which connects to the plumbing drain line and then connect my dump pipe to that. This allows me shut off the dump flow while leaving the gray/black valves open. Don't panic yet, I'm not contaminating grey with black. If I see I've got a black blockage I close all valves, wait until the flow stops and then close the accessory valve. Then I open the grey water tank until the pipes are full, usually gurgling followed by silence. Then I open the black water valve. The pressure of the gray water is greater than the black and the gray water backflows into the black tank. I wait a about 30 seconds, then close the gray water valve and then open the accessory valve.

This works great for me, never failed to clear a black blockage in seconds.

[ktmrfs]

Old-Biscuit wrote:
I have permanently added an 'extra' valve on trailer dump line for many years/several trailers.

I use it to back flush black with grey
I use it to combine grey/galley
I use it to combine all three...black/grey/galley for extended camping

Waste tank is a waste tank..grey is just as nasty as black.


The type of TP is not your blockage issue.

Liquid to solids ratio is.......need more liquid and dump when tanks are near full (fuller the better....high volume/weight increases the 'whoosh' factor)

x2. I use first and second combo's quite often.

[12thgenusa]

jjrbus wrote:
Nothing dissolves in the toilet because there are little bacteria working. A healthy black tank should be a seething cauldron of bacteria!

Not true. It's a holding tank, not a septic tank. You fill it, you dump it. It does not have time for the seething cauldron to develop. Adding septic tank treatment to a holding tank is based on a misunderstanding of how things work.

[jjrbus]

Nothing dissolves in the toilet because there are little bacteria working. A healthy black tank should be a seething cauldron of bacteria!

Just had an issue, knew it was going to be a problem when I hooked up. Rv park sewer is too high. solid's quickly back up and block drain as water goes through, have to lift hose at RV and keep lifting towards drain.

Looked in toilet with flash light, sure enough a pile in bottom of tank. filled with water and drained again, lifted hose from RV to drain. Filled tank and dumped again, lifted hose at RV to sewer and finally success.

[12thgenusa]

Couple of points.

1. Nothing ever really dissolves in the black tank. If you don't believe it, just leave your contribution in your toilet at home and see how many days it stays there without dissolving. :E

2. As a most-of-the-time dry camper/boondocker, fresh water and tank conservation are of utmost importance. Even so, solids are always flushed with a full bowl of water. IF using a little less water really is the clog problem (still not convinced) I will gladly pay the cost with a little back flushing once in a while at the dump.

[Lantley]

12thgenusa wrote:
You guys talking about not using enough water are barking up the wrong tree. It's a plumbing problem not a water problem.

The OP's trailer is probably plumbed in a similar fashion to mine. The black and gray tanks are side by side with the drains on the sides of the tanks facing each other and are are coupled with a tee. From tee there are two more 90 degree turns before the exit point. So waste has to essentially make four 90 degree turns within a very short span. Flow rate and velocity are greatly reduced as a result.

I've been doing as the OP suggested for years and it works great.

Those of you that have a tank with a straight shot out the end won't have this problem.

More water is the solution you will get a better initial flush with more water.
Just imagine putting in more paper than water youir are bound to get a clog.
Now picture using a lot more water than paper. The paper will dissolve.
Not dissolving enough add more water.
I do use the grey water back flush technique but I use it to help clean tank. My black tank does not clog. If your black tank routinely clog you are doing something wrong or your rig is plumbed improperly

[RollandB]

2oldman wrote:
Perhaps you need to use more water when flushing.

Completely agree. We have a pretty large black tank and can easily go over a week with the two of us are out. We collect the dish rinse water in a tub, then dump it and the soapy dish water in the toilet. Never have too little liquid in the black tank.

[djgodden]

Ron3rd wrote:

12thgenusa wrote:
You guys talking about not using enough water are barking up the wrong tree. It's a plumbing problem not a water problem.

The OP's trailer is probably plumbed in a similar fashion to mine. The black and gray tanks are side by side with the drains on the sides of the tanks facing each other and are are coupled with a tee. From tee there are two more 90 degree turns before the exit point. So waste has to essentially make four 90 degree turns within a very short span. Flow rate and velocity are greatly reduced as a result.

I've been doing as the OP suggested for years and it works great.

Those of you that have a tank with a straight shot out the end won't have this problem.

Good point!

Ding ding ding ding ding ding ding... winner!

[doxiemom11]

We've used regular toilet paper (just says septic safe on it) 2 ply for 6 yrs full time and never a clog. We do use generous amounts of water when we flush.

[Old-Biscuit]

My 5vr black tank, grey tank and galley tank drains ALL come out the side of tanks.
Connect to a common drain header that then makes a 90* turn runs 4' and makes another 90* turn before reaching end cap.

Never had a blockage issue.
Black tank and drain header are 3"....if any problem it should be with the 1 1/2" grey drains.

Water to stuff ratio.........high volume/weight-----WHOOSH

[Ron3rd]

12thgenusa wrote:
You guys talking about not using enough water are barking up the wrong tree. It's a plumbing problem not a water problem.

The OP's trailer is probably plumbed in a similar fashion to mine. The black and gray tanks are side by side with the drains on the sides of the tanks facing each other and are are coupled with a tee. From tee there are two more 90 degree turns before the exit point. So waste has to essentially make four 90 degree turns within a very short span. Flow rate and velocity are greatly reduced as a result.

I've been doing as the OP suggested for years and it works great.

Those of you that have a tank with a straight shot out the end won't have this problem.

Good point!

[12thgenusa]

You guys talking about not using enough water are barking up the wrong tree. It's a plumbing problem not a water problem.

The OP's trailer is probably plumbed in a similar fashion to mine. The black and gray tanks are side by side with the drains on the sides of the tanks facing each other and are are coupled with a tee. From tee there are two more 90 degree turns before the exit point. So waste has to essentially make four 90 degree turns within a very short span. Flow rate and velocity are greatly reduced as a result.

I've been doing as the OP suggested for years and it works great.

Those of you that have a tank with a straight shot out the end won't have this problem.

[pauldub]

Are you camping with hookups and leaving the black valve open all the time? That's the most common way to cause a blockage problem.

[Ron3rd]

In an ideal world we would never get a clog, but it does happen. Your method, the Flush King, or the Camco device all work for back flushing. BTW the vast majority on this forum do not use the "RV" toilet paper either.

[Old-Biscuit]

I have permanently added an 'extra' valve on trailer dump line for many years/several trailers.

I use it to back flush black with grey
I use it to combine grey/galley
I use it to combine all three...black/grey/galley for extended camping

Waste tank is a waste tank..grey is just as nasty as black.


The type of TP is not your blockage issue.

Liquid to solids ratio is.......need more liquid and dump when tanks are near full (fuller the better....high volume/weight increases the 'whoosh' factor)