Vannautical engineer
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A while ago I bought one of these filler caps to cap off my water fill hose. I know it's meant to be mounted on the exterior of an RV, but I just needed a fill cap that would fit into my 1 1/4" filler hose and cap it off when I wasn't using it.
I was disappointed to discover that this cap is not water tight. (Obviously it has a vent too, but I'm not talking about that or using that vent. The fill cap itself is not water tight.) I guess that's not a big deal in most applications, but my water fill hose is not much higher than the tank itself, so it's feasible that with a full water tank, when the water shifts around while driving, some water can find its way up to the fill cap and leak out.
However today I figured out a way to make it water tight, and I thought I would share in case anyone else needs an actual water tight filler cap for their water system.
Firstly, I removed that mounting flange around the filler spout itself since I have no use for it. It easily twists off. So that is why my fill spout pictured below does not have a flange on it any more. Not really essential to making it water tight, but just a heads up.
Next, pop the tether for the cap out of the small hole in the top of the cap. Now, cut a piece of bicycle tube rubber to fit inside the under side of the cap. When trimming a rubber circle out, get the size close but a little too big, and then stuff it inside the cap and see where it's too big so you know where to trim it to get it to just the right size. The rubber piece should fill the entire under-side of the cap. Don't trim it down too small or you may have leaks.
Next, sand down the top of the filler spout that the cap goes onto. The added thickness of the rubber makes it so you cannot twist and lock the cap in place on the spout, so you need to slightly sand down the spout to compensate for this thickness. Be careful sanding! I advise using a power palm sander if possible to get a nice even sand over the whole spout. If the sanding has high and low spots, it might leak. And also retry the cap on the spout with the rubber inserted frequently as you sand. Do not sand off too much. You want the rubber disc to get compressed against the top of the spout as you twist the cap shut. If you sand off too much of the spout, the rubber will not get squeezed against the top of the spout, and it may leak.
Also note that by putting the rubber disc underneath the cap, this covers up the hole in the middle of the cap that the tether went though, so water can't leak through there.
Once you have sanded down the spout just enough that you can twist the cap onto it with the rubber disc installed under the cap, that's it. Viola, the cap is now water tight and won't leak.
I was disappointed to discover that this cap is not water tight. (Obviously it has a vent too, but I'm not talking about that or using that vent. The fill cap itself is not water tight.) I guess that's not a big deal in most applications, but my water fill hose is not much higher than the tank itself, so it's feasible that with a full water tank, when the water shifts around while driving, some water can find its way up to the fill cap and leak out.
However today I figured out a way to make it water tight, and I thought I would share in case anyone else needs an actual water tight filler cap for their water system.
Firstly, I removed that mounting flange around the filler spout itself since I have no use for it. It easily twists off. So that is why my fill spout pictured below does not have a flange on it any more. Not really essential to making it water tight, but just a heads up.
Next, pop the tether for the cap out of the small hole in the top of the cap. Now, cut a piece of bicycle tube rubber to fit inside the under side of the cap. When trimming a rubber circle out, get the size close but a little too big, and then stuff it inside the cap and see where it's too big so you know where to trim it to get it to just the right size. The rubber piece should fill the entire under-side of the cap. Don't trim it down too small or you may have leaks.
Next, sand down the top of the filler spout that the cap goes onto. The added thickness of the rubber makes it so you cannot twist and lock the cap in place on the spout, so you need to slightly sand down the spout to compensate for this thickness. Be careful sanding! I advise using a power palm sander if possible to get a nice even sand over the whole spout. If the sanding has high and low spots, it might leak. And also retry the cap on the spout with the rubber inserted frequently as you sand. Do not sand off too much. You want the rubber disc to get compressed against the top of the spout as you twist the cap shut. If you sand off too much of the spout, the rubber will not get squeezed against the top of the spout, and it may leak.
Also note that by putting the rubber disc underneath the cap, this covers up the hole in the middle of the cap that the tether went though, so water can't leak through there.
Once you have sanded down the spout just enough that you can twist the cap onto it with the rubber disc installed under the cap, that's it. Viola, the cap is now water tight and won't leak.
