Can I tie in a shower drain pipe into a washing machine drain pipe? And does the shower need to have a trap?

When washing clothes some water back flows, this problem just started last night. I wash all clothing in cold water , never use the hot water . What is the best method to fix the problem .

The drain pipe for the washing machine with our old washer would overflow on the spin cycles... we bought a new washer and it still overflows.. now we are using Stormbag - Sandbag flood to that overflow. The pipe is only 1-1/8" we have snaked the pipe, used chemicals, even used the bladder (which...

I've had to route my washer drain out of my septic system (drain fields are bad). In the house crawl space the washer pipe 2" pvc came through the floor one bend (elbow) and 3' of travel to the septic cast iron pipe down to the septic tank. I cut into the pvc just past the elbow (maybe 2' past)...