Hello Friends,
Firstly, a "Thanks" for the original responses and recommendations from edbluejuice, N2-UK and Fatboy35. Secondly, an apology for the time it's taken to write a follow-up to this. Before, I get into the nitty-gitty, you'll be pleased to hear that I did manage to clean the fresh water tank in the end but felt that I had to replace the submerged water pump, Which all-in-all, was a great result as I really wasn't looking forward to the cost or hassle of buying and changing the tank.
Anyway, this is what worked for me. Obviously all the work was done on the "fresh water tank" which I'll call the tank from now on. Unless otherwise stated, all filling was done through the large round access lid in the top of the tank and more importantly, ALL EMPTYING was done using the lever to open the drain at the BOTTOM of the tank. The taps were NEVER used until I was sure the water was the best it could be.
1. The Emptying Stage.
I put an old washing-up bowl under the van and emptied the tank with the drain-lever, letting all that yummy green diesel empty out (as it did so it gave me just long enough to close my eyes and shake my head in disbelief just one more time :blg). I walked the bowl down the village to my local garage who kindly disposed of it in their fuel/oil dump.
2. The Removing Stage.
Next I removed as many bits from in an around the tank as I could, without having to remove the whole thing or any of the wardrobe. This included the external filler-cap, the large internal round access lid, disconnected the spade connectors and removed the submerged water pump and as much of the piping from inside the tank as I could by getting my hands in there. The crimped clips on the pipes were a pain to get off, I think I had to hack-saw at least one or two. In the end, I did not remove the pipe from the external filler cap to the tank. What I took off went into a bowl for later.
3. The Boiling Water Stage.
As the tank plastic was heavy-duty and at that stage I figured I'd probably be buying a new tank anyway, I decided that the best way to remove as much of the oily diesel was with boiling water and some washing-up liquid. So I boiled a couple of kettles and poured them in. Then, I drove a hundred yards up the village and back to slosh it about. When I got back I took a washing-up brush and scrubbed the whole inside of the tank as best I could (leaning in through the wardrobe) and then drained it. I think I did this about five times in all. Don't forget to use some of the fresh boiling water for a mug or two of tea. Although, it was by no means fixed, it smelled a LOT better already.
4. The (unplanned) Waiting Stage.
Now, I'm not sure if this helped but I'll mention it anyway. As we'd (well, I say we ...) had this little accident in the winter, we weren't really using the camper. So after I'd done the initial damage limitation, I decided to spend a day or so thinking through next steps. Anyway as usual, other things in life crop-up and unfortunately I wasn't able to do anything else for another few weeks. On reflection, I was wondering whether leaving the tank open after the swill-out gave it a chance to breathe and some evaporation to take place. So this MAY have helped.
5. The Chemical Stage.
During the few weeks following Stage 4 I happened to be discussing my problem with a guy from the village who works with dairly cows. It seems that they have a similar challenge (no, not wives filling the milk tank with diesel) in cleaning residual milk fat off the [milking] equipment: pumps, tubing etc and so they use a strong detergent / de-greasing agent which is suitable for food use. Can you imagine the light bulb appearing above my head? So he agreed to let me have a couple of litres to see if that would help, as long as I was realy careful with it. In concentrate, it's a very strong alkaline that you MUST not get on your skin. Usually used 150/200ml to 20L water (1:100) but after some discussion I decided to go with 1:10 to really give the diesel a kick. FYI. It's called "MEGA-KLEAN DX Tank Cleaner" containing a no messing mix of Sodium Hydroxide and Sodium Hypochlorite, produced by a company called Fabdec.
So wearing some of those disposable, shoulder-length, long gloves used by farmers and vets to do watever it is they do with a cow's rear end, I mixed up some of the detergent with water and poured it in the tank. Again, driving up the vilage to slosh it about a bit. Don't forget to screw the round tank lid back on and stuff any other pipe/cable holes with paper / cloth to avoid it splashing out. When I got back, I used a washing-up brush again to scrub all round the inside of the tank (in my attractive gloves, of course). I did this two or three times, after each, using a hose to top-up the water tank in order to dilute the solution before draining it out. I also used the strong (1:10) mixture to rinse and brush-scrub: all the pipes I'd removed from the tank, the tank lid itself, the tank filler cap and down the pipe from the external filler cap into the tank.
Once, I'd done that pretty much everything smelled soooo much better. I did try to scrub the water pump too but this was too far gone so I spent £30 or so getting a replacement. This was a small price to pay for what (I think) I saved overall plus I knew that at least the pump would be uncontaminated.
6. The Rinsing Stage.
Once all the washing work had been done, I filled and drained the tank a coupe of times with clean water and then did the same with a normal concentration of Puriclean (for cleaning freshwater storage systems in caravans and boats etc). As it was smelling prety good by that stage, I fitted the new water pump, connecting the wires and tubes (with new jubilee clips) and ran some of the second batch of Puriclean through the tap too. I left that in a few days or a week. Finally, I ran a couple of tanks of clean water through the whole system.
7. The Tasting Stage.
Following the last clean-water rinse, like some mad scientist I couldn't wait to experiment on myself and take the taste test on the water from the camper tap... it smelt OK... and to my shock it actually tasted OK too! Amazingly, no after-taste on the palette. As Paul Hogan once said "...like an angel crying on your tongue". We used the camper all the following summer and neither us or the kids complained about the water taste, got ill or grew an extra limb, yet.
So, it all worked out for me but it did involve a lot of effort in the washing, sloshing, brushing and rinsing, which was to be expected. I'm not sure that I could've cut any corners on this as it all played its part in getting rid of the fuel residue. The MEGA-KLEAN detergent played a major part in the cleaning but for most folks, this is something that would be a challenge to get hold of as it's quite a specialist product and also pretty unpleasant in concentrated form, so not to be taken lightly. It's possible that an alternative detergent could be used or maybe a case of more rounds with the washing-up liquid. Finally, I didn't look into the cost of getting it cleaned professionally (if this is even an option), buying a new tank or getting the whole thing swaped out professionally so I'm assuming that my efforts saved a chunk of change (it just cost me my time and the new pump).
I think I've covered everything and hope my experience helps anyone with the same problem. Any questions let me know.
Cheers until next time ... oh wait, that's not what I meant !
YLT4