Fresh water tank access hatch

On Tuesday I lay under the van trying to unscrew the large drain cap on the bottom of my fresh tank in order to clean the level sensors. It appeared to be a simple job but I could not get the cap to budge. Rather than apply excessive force I emailed A/S to ask if it was sealed. Alan Curry sent me a helpful reply saying that thr caps are sikafexed as well as screwed and are really difficult to remove and must be replaced with Sikafex or similar on the threads.
He also said that the sensors are like cavity wall plugs and would pull out once unscrewed. However, because of scale it is unlikly that the screws csn be slackened enought to be able to pull them out without holding the nut inside - which means removing the cap!

This may explain why A/S charge so much to fit a Shurflo and why it would be cheaper to use the submersible pump as a pickup for the Shurflo!

I don't know whethef to put a huge stilson on the cap or to.just buy 500g of citric acid and ignore ever opening tbe tank!
What is the point of a cap if it cannot be used easily for access?

Hi Ron

First off, our van doesn't have an inspection cap so your logic about the cost of fitting a Shurflo doesn't apply here. I think it's more likely because they have to drop the tank, which involves the use of the ramp and takes a considerable time.

If it helps you decide, a previous van had an inspection cap, and it had no Sikaflex in the threads but it leaked from new. Not very fast, but enough to be significant over a week or more. (I wonder if that's why they started using the Sikaflex - which seems like overkill to me as it makes the seal virtually permanent. )

Every effort to stop it leaking failed until I put a tiny smear of non setting builder's caulk on the threads. This stopped the leak, but made it very difficult to remove later, and caulk is nowhere near as "grippy" as Sikaflex!!

It might be better to leave well alone and use the citric acid method. With our van (and probably most recent models) there would be no option anyway as I haven't got the dreaded cap, so it leaves you no worse off and possibly saves damaging the tank and/or starting a leak that proves difficult to fix.

Hi Ron

No consolation to you I know but our hatch has never been sealed with anything, has never leaked and agree with Dave what is the point of putting in a removable hatch and then sealing it! It has been on and off several times. There is a product similar to plumbers mate which you could smear around the threads (never goes hard) and that would stop any leaks or even some ptfe tape would probably do the trick?

Ironically I have just cleaned all the sensors in our tank and am about to refill it, I have siliconed round the part where the sensors go in but the fittings are not very convincing are they, I will be amazed if one of them doesn't leak!

If it were me I would be inclined to try a little force then clean it all up really well and try the above, the hatch to me is so useful and in the worst case if it all goes horribly wrong you can always seal it back on!

David

Hi Ron
When I seal simular joints I always use a good smear of vaselene but always clean the threads and any seal thoughouly. Tighten well and I have never had any problem
Gef

It is a real dichotomy!  It is tempting to leave well alone and go down the citric acid rouite but that does not help me if the pump gives up at some stage.  I am totally happy with Whale submersibles (unlike some folk) so would probably replace with another if it did go - and as a temporary fix I have a spare on my Whale filler and, access cap willing, could do it on the spot.  I always seal that sort of thing with something non-setting or, if there is a sensible seaing washer - which I hop ethere would be, simply put a couple of blobs of silicone sealant to stop accidental unscrewing.
A dichotomy! 

Hi Ron
Ours was sealed (in theory at least) by a massive 'O' ring.

I never found the cause of the constant drip, but it must have been a flaw in the casting of either the tank or the cap. Tightening it until my eyes bulged still didn't seal it, so I had to resort to caulk. Vaseline worked for a while, but then it started dripping again.

As far as the submersible pump goes, if yours is working OK, and if you can get the cap off so the pump could be fairly easily replaced in the future, I would say stick with it. Ours was a pain in the backside every time I filled up after draining down, and rather than risk a total failure on holiday in France, I forked out for a Shurflo. It does give more pressure which is noticeable particularly when taking a shower, but the submersible was fine - when I got the swine to work!

Getting the cap off or not is the decider. If it's sealed with Sikaflex I wonder if you will succeed???

Getting the cap off is  indeed the question and if it does come off, will it be possible to get the seal clean enough to be fully waterproof again? I would certainly be inclined to have a go as the worst case scenario is you would have to Sikaflex the cap back on.

Just refilled my tank having drained down, cleaned the gauge points, I was seriously concerned they would leak as the silly rubber bung fit is so 'sketchy', they didn't, nor did the hatch but now I have a leak from the drain pipe. Guess that means draining it all again cleaning off all the gunk and maybe Sikaflex the pipe back in... something for a warmer day I think?

The whole arrangement could be so much better couldn't it!

I have had a problem with a leak from the access hatch and unscrewed it to check the condition of the o ring on the cap.. all looked ok, on closer inspection of the collar that is screwed and bonded to the tank it became obvious that there was a leak from one side.
 I removed the collar, cleaned it up sealed it with silicone rescrewed it back on but some of the screw holes had stripped and I had to add some more screws, it is now watertight for now, but it seems like a poor design to simply screw a hatch fitting to a plastic tank with a wall thickness of a few millimeters, if I have problems again I may look into fitting some Rivnuts to the tank to give it some strength? luckily the cover removal was straight forward, any sort of bonding on a thread with such a large diameter is always going to be a big problem

The Sikaflex used here doesn't set. If you warm the cap by giving it the close attention of a 2kw fan heater for 20 mins or so you should be able to undo it. CAK Tanks supplied me with the correct sealant

Peter Brown wrote:The Sikaflex used here doesn't set.  If you warm the cap by giving it the close attention of a 2kw fan heater for 20 mins or so you should be able to undo it. CAK Tanks supplied me with the correct sealant

TERRIFIC, Peter.  As always, you come up with relevant and vital information.  You should be paid by A/S for all the work and queries that you save them! 

PS (added later)  Was it SIL310 or SIKA710 that they recommended?  It looks like the latter but SIL310 mentions hatches (probably selaing the fixed part to the tank though)

It is the 710 which is a Butyl Sealant

Thanks again, Peter.  That is what I thought.  This evening I played a heat gun VERY carefully and from a distance around the cap and, EUREKA, it came off.  Once I had felt the first trace of movement it came reasonably easily, there was not too much sealant in the threads and what was there peeled off easily.

Brilliiant.  Now two huge votes of thanks (NOT!) to Auto-Sleepers. 

1:  Just as well that they used the sealant.  There is a massive O-ring in a groove in the cap - They had not lubricated the edge of the O-ring with the result that it had come out of its groove in two places!  .  It is reuseable but it is unlikely to seal without sealant on the threads.

2:  With all the space of the tank that is available they have put the sensors close to one end, almost as far as possible from the access cap, presumably to economise on the wiring to the sensors.  Luckily I am slim and my elbow JUST went through the hatch.  At full reach I could just touch the sensors so I have given them a brush with a stiff bristled brush. I will have another look with a mirror once I receive the LED worklight that I ordered yesterday from Amazon.  I will also look to see how the pump is installed

I wil obviously need some 710 sealant and I hope that I may also be able to get hold of an O-ring (or 2!) from CAK at the same time.

Thank you once again for your encouragement.

I unscrewed the tank cap when I fitted a Shurflo pump to my Nuevo.
The cap unscrewed relatively easily using 2 hands but as I could not even get my hand inside the tank hole I just left the old submersible pump in as a pick up which worked fine. 
The cap did not have any sealant on it and I just screwed it back on tightly.