Can I ensure no leak in fitting before adding to system?

[Alan M.]

I am replacing an elbow fitting on the cold water side of my RVs aluminum hot water tank. First I replaced a plastic elbow with another plastic one, used RectorSeal pipe sealant, reconnected to pex piping and it leaks at the threads connection to the tank. Max psi is 55 in the line.

Next I am thinking of using a brass elbow with pipe tape sealant.

Question: is it possible to be sure the seal of the fitting to the tank will not leak before I connect all pex fittings and power up the pump?

It's a 1/2 inch standard thread connection to tank.

Note, obviously I am very inexperienced at this and would appreciate your advice on how to not just create another leak.

Happy New Year and thanks.

 

[Phog]

You need to be careful with an aluminum tank, it is very easy cause galvanic corrosion of the aluminum by mixing in components made of other types of metal. Having dissimilar metals in contact with each other in the presence of water actually makes an electric cell that drastically increases corrosion. Aluminum makes such a cell will almost every other metal. I suspect if you install a brass fitting, it would quickly rot out the tank all around where the fitting screws in. So I would stick with plastic if you can. Perhaps try a different plastic fitting, and also maybe a little wicking along with the thread sealant like the old timers used to -- wick is just a thin strand of hemp rope, you wrap it around the threads in a spiral and it helps fill the voids (you can find DIY instructions on YouTube).

Also I'm not familiar with RV water tanks but just want to confirm that this is not a face seal fitting that needs a gasket. (Home plumbing is almost always NPT tapered pipe thread, but tapered threads are not the only way to make a seal).