Please help - Black water holding tank damaged

Some times it is hard to determine what the tank is actually made of. I would get some MEK and dab some on both the tank and pipe if the solvent softens the plastic material the Plastic Mend or other solvent based adhesives will work, the solvent with partially dissolve the plastic then flash off leaving a good chemical bond. If the tank is made from polyethylene the solvent based adhesives wont work, there you need a mechanical bond and need more bonding surface so a wide flange as someone else suggested is a good idea.

texnwar wrote:

ScottG wrote:
That is ABS. Dont use anything except good old ABS cement.
Clean everything well and use the cement. Unless there's some piece missing you dont need to add any material - that will just make the job harder.
Hold in place for 30 seconds after cementing and your done.
It will last forever if done right but if you use some other "glue", it will eventually fail.

The tank is plastic after all, not fiberglass like I first thought. From what I understand after doing some research, ABS or any other cement for that matter may not work. It's suggested to weld the cracks via polyethylene rods.

Don't get the tank and the pipes confused. You are correct that if the TANK is cracked or broken it needs to be welded back together by someone who knows how to use the polyethylene rods and has the proper equipment. What you are showing to be broken is the ABS pipes that are attached to, but separate from, the poly tank.
If you can follow that pipe back to where it connects to the tank it may just be held to the tank with a clamp or 2 and you could repair the entire run like new.

When I had a leak in my black ABS holding tank I used Plasti-Mend.

If you do not want to future problems replace the tank.

It most likely has other problems not evident right now.

I'd suggest to grind/sand the broken fitting area to as flat as possible. Treat the tank area that is to be patched with a good cleaner/primer. Install an ABS fitting with flange over the hole in the tank, using ABS cement. The ABS cement is a solvent welding adhesive. It actually melts the pieces it comes in contact with. Be scrupulously clean. The advice to use a rubber coupler has a lot of merit. It may save your new work from suffering the same fate as the original.

Hard to see from here, but for a repair that large I'd consider removing all the old excess glue (*if* you can) and what's left of the protrusion for the fitting and put a patch over it all. If you go to a local plastics shop you can get a piece of sheet ABS or find an online source. It's available in 1/16" to 1/4" like in this website for example. ABS sheet can be bent/formed with a heat gun. To remove the old cement, try a heat gun to soften it and use a scraper, small sharp chisel and/or utility knife.

The Plasti-mend method might be the way to go but will it work over old ABS cement? If you can remove the old cement where you need to down to clean ABS, re-attach the old fitting with cement and then patch the missing/damaged portion with the Plasti-mend patch kit?

The original tank wall will flex somewhat when full and if travelling with contents in it. If putting a patch piece over it, iIt might be a good idea to avoid sharp corners and make the patch piece as rounded as possible to reduce stress points.

There's a number of RV holding tank manufacturers online that have fittings and info. There are some youtube vids showing how to do tank repairs that may or may not help much.

It would be nice to see some photos after the repair.

FWIW, are the tank sensors not installed at the recommended elevations? Looks as if there isn't much change in elevation between them. Not uncommon.

3m eraser wheel clean it good order a plastic welder kit off anazon and weld it in be done with it

texnwar wrote:

ScottG wrote:
That is ABS. Dont use anything except good old ABS cement.
Clean everything well and use the cement. Unless there's some piece missing you dont need to add any material - that will just make the job harder.
Hold in place for 30 seconds after cementing and your done.
It will last forever if done right but if you use some other "glue", it will eventually fail.

The tank is plastic after all, not fiberglass like I first thought. From what I understand after doing some research, ABS or any other cement for that matter may not work. It's suggested to weld the cracks via polyethylene rods.

I don't know who you are talking to, but I would bet like Scott said that tank is ABS which is technically a plastic and the best repair is actual ABS cement which generally you have to get from a decent plumbing supply store. Many FW and all waste tanks that I'm aware of in RVs are ABS and while many of the universal "plastic" type plumbing cements will work O.K. on holding together ABS slip type fittings for the strongest repair I recommend real ABS cement. Big box stores won't carry it except via special order. True ABS cement has actual ABS material dissolved in it and the bonding is solvent based so proper repairs are nearly as strong as the original.

Here is what the OATEY ABS cement looks like:



For a repair like you are looking at I would first after thoroughly cleaning everything cement the two parts together with real ABS cement and once that is somewhat cured I would build up the tank to pipe interface area with multiple coats of a mixture of the real ABS cement and ABS shavings which you can make by filing or making multiple cuts on a sacrifical ABS section of pipe or fitting and mixing the ABS filings with the cement to make a thick paste just before applying it to the repair . This will strengthen the overall pipe to tank junction since once cured that ABS/shavings mixture is basically just ABS material itself and by extending that mix up further onto the pipe and tank you will increase the bonded area of the repair. It might take up to a week for a 1/4 inch thick layer of ABS/shavings mix to totally cure since the curing is by solvent evaporation which can be a slow process so putting on 3 or 4 coats could take up to about a month for a really good repair and that is not something any repair place or mobile tech will recommend or do because of time.

Larry

ScottG wrote:
That is ABS. Dont use anything except good old ABS cement.
Clean everything well and use the cement. Unless there's some piece missing you dont need to add any material - that will just make the job harder.
Hold in place for 30 seconds after cementing and your done.
It will last forever if done right but if you use some other "glue", it will eventually fail.

The tank is plastic after all, not fiberglass like I first thought. From what I understand after doing some research, ABS or any other cement for that matter may not work. It's suggested to weld the cracks via polyethylene rods.

That is ABS. Dont use anything except good old ABS cement.
Clean everything well and use the cement. Unless there's some piece missing you dont need to add any material - that will just make the job harder.
Hold in place for 30 seconds after cementing and your done.
It will last forever if done right but if you use some other "glue", it will eventually fail.