Help! I am trying to install an undersink water filter. Its a Rainfresh brand and is designed to be used under sink or as a whole house filter.

It has a plastic female 3/4" inlet and outlet. I have a brass 3/4" male to 1/2" PEX barb and the male to female brass to plastic connection consistently leaks. I used teflon tape - at first a lot, then a little, and it leaks either way. What am I doing wrong?

See the fittings below.

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Some of those filters require a rubber washer to be installed in the filter housing before you screw in the male adapters, they don't seal with the threads. I'm not saying that's the kind you have, just that it's possible. Other than that just make sure you're wrapping the tape in the correct direction on the adapter before screwing it in.

I wondered that. Do I just use a garden hose type washer? Or is there a special type of washer for this sort of application. The filter came with no fittings at all.

Thanks in advance.

Like these I guess?

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Edited 2 times.

The instructions that come with the Rainfresh filters say to tighten the pipe threaded fittings one to two turns after they are finger tight and that is totally inadequate. It takes about five turns to get them leakfree. I don't use washers.

I like to make up the joints to the filter and test with compressed air for leaks before I actually install the filter and run water through it.

If it didn't come with washers, then they are probably not required in your filter, but those are the washers I was referring to.

The threads in your pic, while hard to see, do not appear to be tapered pipe threads.

The male PEX adapter is tapered pipe thread.

Use the washer AND 2 wraps of PTFE (Teflon) tape.

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