I think this is what you are looking for , they also do an add on to the kit which consists of a holding tank for the waste , it has a float valve fitted so when the tank is full a booster pump kicks in and this goes back through the RO , that was a bit of a crude explanation but i am assured it works , they have had a couple of units on trial with a council up north for some time , results are promising so i am told , there was at first concern over the life span of the filters but this too im told is better than expected
Rich