Frozen septic system - HELP!

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Well-known member
Mar 16, 2009
Sacramento area
My 30' Salem 5th wheel is in Tahoe. The temps 2 weeks ago were down to -17! I don't keep water in the pipes, since I don't keep the heat on when I'm not there (I'm there on weekends). I bring a few gallons of water each weekend for drinking, washing and flushing.

When using the toilet, I pour in a cup or two of water to flush.

After the big freeze, my toilet flapper wouldn't open. I removed the toilet (Thetford Aqua Magic IV) and found the toilet mechanism was jammed with frozen pee and poop. Also, the 3" pipe that leads down to the black tank was full to the top - again it was frozen.  I ran a heater in the bathroom and a heater in the basement area where the 3" septic pipe leads from the toilet to the black tank. The stuff in the pipe that you could see with the toilet removed melted to liquid, but wouldn't drain.  I ran a 3' "toilet snake" down the pipe but I couldn't tell if it made it into the tank, but still it wouldn't drain. It's possible, but VERY unlikely that the tank is full, since it's only my wife and I and we only spent 5 or 6 nights in the trailer since the last time it was drained.  And I can't drain it anyway, if it's frozen.

The pipe leading from the toilet to the black tank is 3" diameter, has 2 45 degree bends, and is about 2 1/2 feet from the toilet to the black tank.

So now to my question - is there a flapper of some sort where the 3" pipe from the toilet goes into the tank? It's possible that the flapper is frozen shut. I guess it's also possible that the tank is frozen and blocking the intake. When I left on Monday, I left a 75 watt drop light in the basement cabinet to warm up the 3" pipe going into the tank. My buddy checked today and it still hasn't drained. The temps are down to freezing at night, but up to 40F during the day (pretty warm for Tahoe winter).

Any ideas that might help? Is there a flapper of some sort where the intake pipe meets the black tank?

The only two ideas I can come up with are: 1. getting an engine block heater (one of those heated dipstick things), but I'm not sure if that will provide warmth at the very end of the dipstick, where I really need it. 2. wrapping some pipe heat tape on the lowest part of the intake pipe and hope that will heat things up enough to break up any ice.

Thanks for any ideas!
The amount of water, "copious amounts" that you should use when flushing doesn't change just because it's freezing outside. So, the backup you have is a predictable event. Now, add in the freezing component and the unclogging is complicated by the potential that at any point in the system there could be an ice blockage. 40 degrees each afternoon isn't enough to thaw all the pipes. If it didn't melt all the snow, then it wasn't warm enough to melt the ice in your system.

IMHO you're best solution is to tow the unit back down to wherever you live and wait for everything to thaw. Don't be surprised if things like drain valves or even piping is cracked or broken. So check often during the day or two or three that it takes to thaw. Once everything is thawed you'll want to drain the tank so you know it's empty. Then you need to mechanically break up whatever clog may be in the pipe from the toilet to the tank. There is no doubt soggy paper and semi-solid feces which needs to get broken up enough to flow down to the tank. Follow with copious amounts of water. Enough water to fill the tank to 3/4 or more. Now take the unit for an hour long drive to agitate and break up the solids, TP, etc. Then drain and flush, fill again, drain and flush. Now check carefully for any leaks you haven't found before.

That's what I'd do, but then my solution to freezing weather is to avoid it, not to seek it.


Ken, worst case scenario, I tow it home, but in the meantime, does anyone know if there is a flapper of some sort at the junction of the intake pipe and the black water tank?
Hi Ho:  Motothomes don't generally have any restriction.  In fact, if you open the toilet drain the tank is normally a straight shot down and you can see how full the tank is.    This is, however, no help for you because a 5th wheel may not be built that way at all.  Sorry.
You may want to go on the Manufacturers internet website and look for plumbing diagrams.  I have a Winnebago and their website allows owners access to plumbing and electrical diagrams by year and model. These manuals and diagrams are available to the general public without having to register on their site.  You might even just look at the Winnebago TT diagrams as it's likely that all manufacturers use similar plumbing methods.
I have a couple of the 45 bends in mine also.  Try using a hair dryer and start as close to the tank as possible and heat upwards.  It will start as a trickle and as soon as you get a small amount of water running thru, go back on top and flush with hot water.  That may open it up.  I had to do this a few times  on  a mobile home wwhen to sewer line frooze due to a slow leaky faucet.
My guess is that you have created the dreaded poop pyramid with your ultra conservative use of flushing water.  I suspect the solids have dropped in place under the pipe until they have risen to block the ability of anything reaching the tank.
If the pipes directly beneath the toilet were clogged as you described, your problems began long before the freeze.  With a "one cup flush", the stuff has turned to concrete by now.  JMHO
ARGGGHH - I had read about the "poop pyramid" in the past, but never thought it would happen to me! I guess I forgot about the need for alot of flush water, since this hasn't happened in the past few years.

I'm afraid this is probably what happened, and the hard freeze just made things worse. I'm hoping a toilet snake, a heat lamp and the current warm(ish) weather can break things up enough to add a bunch of water to the tank, but won't be surprised if I have to haul the trailer to a dump station for a full flush.

Thanks for helping me figure this out.

This is the tool I would use if I were you. They are sold at most Walmarts. Connect the sewer hose to a sewer and open the dump valve. Turn off the water pump in the RV, connect the hose to the tool, put it into the bathroom through the bathroom window, open the toilet valve and put the tool as far down the toilet as you can get it. Then turn on the water SLOWLY. Since the blockage is close to the top of the black tank it might shoot black water back out of the toilet. When you get the top of the pyramid worn away you can put the tool in further and turn the water pressure up. Once you can use full water pressure then plan on it taking at least another hour to clean out the black tank.
i don't know if some rock salt in there might help slowly work its way through. it works to melt ice on roads. also,  i have put icypropyl alcohol in my windshield washer reservoir when i forgot to add winter washer fluid late in the fall. the summer fluid froze solid. my neighbor told me to put the alcohol in the reservoir and it would work it way up the lines to the wipers. it did in fact work and within an hour or so the reservoir was thawed and the windshield washer was working again. you probably have some in your medicine cabinet or can get some at the drug store.  don't know how it would be on seals and stuff but if it worked you could flush the tank right away and get it out. someone else might have an opinion on this. good luck.
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