Non-return valve for water softener overflow - possible?

[larrylamb11]

I am about to put a water softener in and see it needs two 'outlets' - one for the drain when regenerating and one for the overflow from the brine tank in case there is ever a problem.
The instructions call for the overflow to go out through an outside wall and oveflow to atmosphere, but I can't as I don't have an outside wall to go through.
I do have the 40mm wast pipe the water softener drain is going into though (together with a washing machine and basin) and the softener overflow is above the level of the P trap. Consequently I was thinking of hooking the overflow pipe up to a redundant washing machine connection on the P trap so that it overflowed down the foul drain in the event of a malfunction....
Then I got to thinking... if the P trap blocked or the drains backed up, foul water might run back along the overflow pipe and contaminate the brine tank on the softener... which wouldn't be pleasant!
So is there any sort of one way valve that has minimal resistance to allow the free flow of water from the overflow but stop any potential backflow? Something I could fit in line? I checked an ordinary 15mm check valve and the resistance to flow is too high for the atmospheric flow out of the brine tank to overcome.

 

[Nige F]

replumb with a Hep V O waste valve in line horizontally that will stop any waste backup

 

[leakydave]

Ask the manufacturer for advice.

 

[JohnD]

standpipe method, as frequently used with washing machines, will not backup as the top of the standpipe is open to the air.

However if the brine tank overflows, you ought to see it same as any overflow, so that you are aware of thew fault and get it corrected.

 

[larrylamb11]

Thanks for the replies.
Manufacturer said "Weeeell, they very rarely fail anyway... alot of people don't even bother to plumb in the overflow... its up to you really... if you don't have an outside wall, just do the best you can" ....click...brrrrrr...
I have got a Hep VO trap, I will have a look and see if it can be jiggered in there somehow, but the reason it hasn't to date was a lack of deployable space... worth having another look at it though
There is a standpipe for the softener drain to discharge into (I think the drain needs a 20mm air gap) so I realise that if the drains ever back up it will spill over this first, the problem is that the softener overflow level is well below the top of the standpipe - its just above the P trap, so would be the first thing in line to get swamped in the event of a blockage downstream and subsequent backup. Hence why I was looking for a one-way valve on the softener overflow to prevent any ingress of sewage into the brine tank if the worst did occur.
I have never had a water softener before, is failure and overflowing of the brine tank a likely occurence?

 

[JohnD]

roundabout once every ten years on mine.

 

[mysteryman]

Put them both into - or above - a washing machine trap.