Quote Originally Posted by AZDesertRat View Post
1/4" MIP x 1/4" tube size is the most common.

If I might make a couple suggestions. Forget the flush kit, they have no proven documented value other than to lighten your wallet and give you a warm fuzzy feeling. They don't do anything. You would be much better off installing a simple tee and ball valve between the RO membrane and the DI filter as a DI bypass. When you first start making water open this valve and let the first quart or so go down the drain to flush the TDS creep out before it hits your DI and shortens its life. This is proven and has value. Flush kits do nothing for TDS Creep since all they do is pass water around the waste side of the membrane, not the treated side and the volume and velocity is not nearly enough to scour the membrane.

Next, rather than an inline TDS meter you are much better off with a good handheld that costs the same $25 or less. the inline is limited to two TDS readings, usually RO only and final or RO/DI TDS. But, to troubleshoot a RO/DI you need three TDS readings, tap water, RO only and RO/DI so you arestuck with insufficient information. Plus the inlines are not truly temperature compensated and monitor air temperature not wate rtemperature so can be significantly off unless your wate rand air are exactly the same which is rare.

A good handheld is much more versatile, can be used on tap water, RO, RO/DI, bottled distilled, the LFS water, your buddies water, drinking water etc and is temperature compensated so is much more accurate. Good ones like the HM Digital TDS-3, TDS-4TM and their new AP series all have a built in digital thermometer too so serve dual purpose and all are around $25 or less.

My third suggestion is to measure your actual waste ratio using a measuring cup and watch or clock to ensure it is close to 4:1. Most vendors use a fixed flow restrictor and its really not a one size fits all and could be as high as 20:1 wasting water and reducing the RO efficieny or as low as 2:1 fouling the RO membrane and shortening its life driving the cost of ownership up. If it is not close to 4:1 I suggest buying a $5-$6 capillary tube flow restrictor and trimming it to fit your own unique water conditions.
Thank you kindly for the feedback, I really appreciate it. I'm not so concerned about the flush kit really scrubbing the membrane as I am just using it to push the old water out of the system and if it takes some of the build up off of the membrane too, then that's cool with me.

As for the TDS meter I have the dual in-line one, a single in-line, & a handheld. A little redundant, yes, but I like to measure for accuracy.

I have considered changing out the flow restricter to a capillary tube restrictor, however, I will try your test first to see what my waste / good water ratio is (thank you for the suggestion). These are relatively cheap upgrades to the unit so i'm not too concerned there. I just want to make sure things are consistant from the source.