Water softener drain challenge - looking for expert advice

[steve-lion]

Hello all - I'm replacing a 19 year old Ecowater water softener. The softener is in my basement and drains using 1/2" ID PVC that runs overhead about 45 feet before tapping into the main drain line at the point it exists the house to the septic system.

Most every replacement water softener I'm looking at does not recommend running drain lines this distance, without at least upgrading to 3/4" ID drain tubing. Unfortunately, replacing this drain line is no longer an option given that much of my basement is now finished.

My best option seems to be to run a 1/2" or perhaps even 5/8" ID drain line to a kitchen sink located above the softener. Total run would be about 17' and rise about 8'. The sink has a p-trap and vent per code. I'd looking for advice on how to tap into this and make sure I am still in compliance and have no problems. Please see attached image.

I'm thinking I would replace the chrome tailpiece with PVC DWV and tap into it with 45-degree wye and then a straight run out of that to a height about equivalent to the vent (see pic), connect a 45-degree sweep to get it totally vertical, and then finish it with a dual softener / R-O air gap connection. (I might also use this for an R-O drain).

Any issues or suggestions?

 

[Reach4]

Most every replacement water softener I'm looking at does not recommend running drain lines this distance, without at least upgrading to 3/4" ID drain tubing. Unfortunately, replacing this drain line is no longer an option given that much of my basement is now finished.

The makers don't always take into account the gpm of the drain when specifying if 1/2 inch is enough. A 10 inch tank softener only backwashes at 2.4 gpm typically. So the backpressure of what you have is probably ok. The incoming water pressure has an effect to. If your incoming water is 35 psi, then you would worry about backpressure. If it is 55 psi, even a 10 psi (or even 20 ) backpressure would not bother the softener. You could measure the backpressure if you were concerned. If the softener has 30 psi between the input and drain output, it will be happy.

For your idea of going to that sink, you could put a branch tailpiece extension inline with the existing tailpiece. It would be better to use an air gap made for a dishwasher. An RO drain has a very low flow, so the air gap can be small.

 

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[steve-lion]

The makers don't always take into account the gpm of the drain when specifying if 1/2 inch is enough. A 10 inch tank softener only backwashes at 2.4 gpm typically. So the backpressure of what you have is probably ok. The incoming water pressure has an effect to. If your incoming water is 35 psi, then you would worry about backpressure. If it is 55 psi, even a 10 psi (or even 20 ) backpressure would not bother the softener. You could measure the backpressure if you were concerned. If the softener has 30 psi between the input and drain output, it will be happy.

For your idea of going to that sink, you could put a branch tailpiece extension inline with the existing tailpiece. It would be better to use an air gap made for a dishwasher. An RO drain has a very low flow, so the air gap can be small.

Thanks for the excellent advice. My incoming pressure is from a well tank set at 40/60 PSI so I presume 40 PSI would be close to the minimum on the input line on the softener which is only 12' of 3/4" copper away from the well tank. If I tried to use the existing line, any suggestions as to how I would know if it was problematic?

I like your suggestion of dishwasher air gap as these are more readily available. To be clear though, the air-gap I was suggesting supports simultaneous 1/2" or 5/8" ID softener drain connection and a 1/4" R-O drain connection. See it here: https://www.amazon.com/GAP-CAP-Space-Saving-Drain-Standpipes/dp/B01EMC06X2/

 

[Reach4]

I am saying that if you can get 30 psi between the input and the drain output, you will have plenty of pressure for backwash -- the high-volume drain. To measure the backpressure into the drain line, you could figure out some kind of tee.

I like your suggestion of dishwasher air gap as these are more readily available. To be clear though, the air-gap I was suggesting supports simultaneous 1/2" or 5/8" ID softener drain connection and a 1/4" R-O drain connection.

For that, you would need to build a standpipe with trap.

I was suggesting that you could feed into the place you photographed with minimal work.