John Guest 3/8 Inch O.D. Tube Size x 1/4 Inch NPTF Speedfit to Female Shut Off Valve, Push to Connect Plastic Plumbing Fitting, PPSV501222WP

It took me a couple orders before I found this one. There are multiple types and sizes of these. The output is 3/8 here, which is the thicker RO tubing. Some of these valves are only 1/4 output, which fit the thin tubes, so best to check the type of tubes in use on your system here. The other end, the end that fits onto the RO tank-- NPTF is the twist on type. They make multiple sizes of this and despite thinking I needed 3/8 on the bottom, 1/4 NPTF seems to be the more common RO sizing.Use a little plumbers tape on the twist on to ensure a smooth/leak free connection. Screw on by hand as tight as you can possibly get it to go. No leaks yet on two of these. The valve does its job. The price on this is a bit steep for what should be a $3 part, but it works perfect and is the only one out there it seems.

If you need a 3/8” quick connect (push in) water tank valve for your RO line, this is the one you need. I bought a cheaper version about 6 months ago to add a 2nd tank to my RO system. About 4 months later, my wife saw water dripping from the kitchen sink cabinet. The issue was the tank valve I had purchased earlier. The base of the valve that screws onto the tank nipple had split. I was getting a slow but consistent drip from the valve and it ended up ruining the bottom of the cabinet from water damage. I ordered this replacement and it’s clearly made by people who know what they are doing. The base of this valve is reinforced by a brass ring to prevent the plastic from cracking. Works like a charm and I am confident this piece will not fail over time. Spend the extra few dollars to get one that will last.

I added this to a 6.5 gallon RO water storage tank. Easy to attach and no leaks.

Just not the size I needed, that was my fault

I had to replace the water storage tank for my kitchen RO filtration system. The old tank had a different fitting, no valve and no snap-in collet connection. I was wary that this valve would do the job, not being that familiar with collets and generally not that handy.I didn't want to reuse the old fitting because it didn't have valve to shut off the supply, and I wasn't sure if the plastic threads—to the tank and to the water line—would still be any good. Or that I'd strip them while removing it, and be stuck with no water in my kitchen sink until I figure out what the hell to do next.So I took a chance and bought this, having heard good things about the brand. Screwed onto the top of the tank no problem (yes, I was smart enough to use plumber's tape). And the 3/8" water line snapped easily into the collet. The true test was when I turned the water supply back on. No leaks!

Went to Home Depot, went to Menards ... No go ... You would think that I was asking for a magic pony .. Wasted an hour ..Came home, searched, found this, 24 hours later I'm back in business ... Works great for a typical basic house 3 gallon RO system tank ..

This fit the tankRO – RO Water Filtration System Expansion Tank – 2 Gallon Capacity Water Tank just fine and allow me to use a 3/8" water line. Seems high quality, no leaks.

Works well and as expected.