On a similar note regarding a similar thread on Drano: My washing machine’s drain line’s p-trap seems to be clogged with lint. Is it safe to put Drano down this? And, will Drano work? (Actually, I use something a little stronger that advises the use of gloves and goggles, but I cannot recall the name offhand. It comes in a black bottle sold at Home Depot.) Just upstream of the p-trap, there is a 1.5-ft vertical riser open to atmosphere where the drain line off the washing machine just hangs. I can easily remove the washing machine’s drain line and pour Drano down there.
The only other thing you should know is that the discharge off the water softening system drains to the same point when backwashing. Any chance of any siphon action sucking Drano up into the water softening system?