frozen/crack black tank

[rrohrer]

For several yrs now with my older camper I have always left about a gallon of water in the black tank. dumped in after disconnecting along with rv treatment to keep tank clean. I never emptied at end of season with thought- told to me by another camper that this is not enough to cause issue. I looked at my camper and saw some insulation protruding around the sewer outlet pipe and the cover around this area seemed swelled. I got paranoid that tank burst. I'm not sure that's the case and plan to go back with tools remove cover and look. Question- is this unsafe practice. how easy can tank crack? and how could I fix if it is cracked??

[SteveC7010]

For several yrs now with my older camper I have always left about a gallon of water in the black tank. dumped in after disconnecting along with rv treatment to keep tank clean. I never emptied at end of season with thought- told to me by another camper that this is not enough to cause issue. I looked at my camper and saw some insulation protruding around the sewer outlet pipe and the cover around this area seemed swelled. I got paranoid that tank burst. I'm not sure that's the case and plan to go back with tools remove cover and look. Question- is this unsafe practice. how easy can tank crack? and how could I fix if it is cracked??

The concern is that the first gallon or two of liquid in a black or gray holding tank occupies the lowest part of the tank which includes the drain fitting and the dump valve and maybe a couple of inches of pipe between the valve itself and the tank. Remember that freezing water breaks things as it expands in an enclosed area, so it is possible that there could be some freeze damage in that area because part of it is enclosed. If there were no drain, a gallon or two of water simply laying on the bottom of a tank would not be able to cause expansion damage because there is no enclosed space.

My personal opinion is that both tanks should be drained as dry as possible of water before winterizing. When I winterize, I blow out the water lines with the dump valves still open. After letting them drip for a few minutes, I close them up and pump the pink stuff into the system. Typically a few cups of pink RV antifreeze ends up in each holding tank and a bit in the toilet. It should help keep the seals from drying out. And if there is any residual water on the floor of the tank that didn't drain out, the antifreeze lowers freeze point enough that it can not cause a problem.

If one lives in an area where it's possible to camp year 'round, but there still might be freezes, I'd advocate draining the holding tanks as dry as possible after blowing out the water lines and draining the HW tank. If things are clean enough, I'd even think about leaving the valves to make sure no water accumulates up against the valve or in the drain pipe.

[SteveC7010]

Second part of your question: How easy is is to fix a crack?

Well, that depends on where the crack is and how big it is. There is a technique to repair a crack in an ABS tank or pipes that can be quite effective if done properly.

First, drill a tiny hole at each end of the crack which will stop the crack from extending further.

Second, use a v shaped tool (a church key works good or a Dremel Tool) to open up the crack and create some flat surfaces for bonding. The opening doesn't have to be all the way through the pipe or tank wall, but it needs to be deep enough for the repair to hold well. And very, very clean and dry.

Third: There are two ways to fill the crack. I understand there are now some ready made patching kits for ABS available that are used to fill up the crack. Supposedly they work well. Follow the manufacturers instructions on them, but they will be very similar to the next paragraph with the exception of making up your own repair goop.

The second way is a bit more labor intensive, but also very, very effective. Basically, you get a small piece of ABS and use a rasp or similar to make up lots of shavings. Using ABS cement, you mix some of the shavings into a paste and apply it to the crack. You have to build it up slowly with several layers and plenty of drying time in between applications. Some of my friends over on the Sunline forums have done this with great success. The resulting joint can be actually stronger than the original material. I've used the same technique to build stuff out of ABS sheets. It does work.

It's best to do this this repair in warm, dry weather, probably at least 60 F or so.

[rrohrer]

thanks steve. i will no longer be leaving water in at end of season. I think if anything broke it would most likely be the pipe from the tank to the valve. it looks like you can buy some of the stuff- not too expensive. I will know more when i pull at the infamous four seasons sheet on the underbelly. It may very well be nothing at all. I just want to make sure in shape before my first spring trip.