How to weld black water tank?


2015 long/tall limo RV 2.1l
I am doing Sprinter conversion using parts from older truck camper.
My primary goal is to use the parts I have before I spend more money on new parts and here I come to black and gray water tanks.
They are pretty nice tanks, but about 7 ft long and too long to fit into space of spare wheel on my 3500.
I need to make them about a foot shorter and if possible redo the 3" inlet.
Anybody knows DIY technology? Soldering iron?


Van Guru
I designed and CNC'd parts for our black and grey water tanks. They were designed as flats, heat formed and then welded. Pretty innovative if I may say so myself. Thought about trying to weld them myself but upon considering the consequences of a failure, I decided to seak out an experienced plastic welder. The guy did a terrific job and the tanks are going strong for over 8 years. We even took them to a tank blow molder where they leak tested them under pressure and spin-welded on the fittings. Some things are better left to someone with the proper tools and experience.

All the best,


Well-known member
When I cut-n-shut one of my pre-molded tanks I used an air soldering station. Just a crappy one of eBay "Atten 858D". You need to find out or make a good guess at what type of plastic it is, then get some filler rod to match, and find out the temperature to use. Mine was EPMD. Look at youtube to get some ideas and maybe use some offcuts to practice on first.

Mine was the first time I'd done it in anger, and it has been water tight for over 5 years now. This would be about a 1m weld and it turned out perfect. By contrast I am rubbish at TIG welding.


2015 long/tall limo RV 2.1l
When I cut-n-shut one of my pre-molded tanks I used an air soldering station. Just a crappy one of eBay "Atten 858D".
Is that what you are talking about? Cheap enough and can have it in 1 day.


2015 long/tall limo RV 2.1l

I think not bad for 1st such job in my life.
But bear in mind, I did work with torches a lot and keeping the hot end away from the skin become my natural reaction.
Unlike metal welding, most of the heat needs to be applied to rod, who you push into softened material under it.
The 700W soldering station is slow, but that to some degree is good as less chances to melt big hole in the tank.
I worked in the 90-100F weather, so those working in colder temperatures might consider more powerful gun.
So my tanks are basically ready and tomorrow I will start initial installation.


2015 long/tall limo RV 2.1l
I put 6" tall fittings in it and top them up.
No leaks and I will recheck tomorrow morning.
Don't mind small drip at testing fittings.
Black tank measured 22 gallons btw, what is more that I wanted, but that is good thing.

Top Bottom