Drain requirements

I have a 2" ABS drain in the wall of the laundry room which currently has the washer drain pipe and the water softener (copper) drain pipe going into it. The drain goes down the wall, through an S trap, to the main line under the slab. Because of the air gap for the water softener pipe, water splashes out and has damaged the wall. I was thinking about putting in two drain pipes - one for the washer and one for the water softener. Is this possible?
Can I put a Y in above the S trap to make two drains? Is there any requirement for how high the rise above the Y must be before the drain opening?
TIA
- Bob

In Florida, which is based on the IPC, yes. Your tie in above your trap for the washing machine should be above the rim level of your trap. Have you looked into these? http://www.oatey.com/apps/catalog/showskus.asp?ctg=5&subctg=0&prodgrpid=279
Washing machine box with an indirect drain hookup built in.

Thanks! That Oatey Eliminator washer box is exactly what I need. With the part numbers, I can track it down in my area.