My old washer just let the smoke out of the control board in the middle of a load of laundry the other day but luckily I had my moms old washing machine (still newer than mine was) laying around to hook up instead. Except now I realized that my mom aparently loves fabric softner and every compartment on the thing needed a waxy fabric softner buildup scrubbed out of it.
I can't exactly complain about a free appliance but damn do I hate fabric softner. It makes my fabrics water repelant and it gums up washers. Awful stuff.
I recently read an article (in Dutch) which sums up why you should not use fabric softener. It is quite politicized, so I will not directly link to it here. The TL:DR is a bit like below:
I feel the same way with my wife adding fabric softener or natural vinegar to loads. I would expect the vinegar to throw off the ph of the water and make the detergent not work as well as it's supposed to.. but to each there own I guess.
I always throw vinegar into the fabric softener compartment so it's dispensed toward the end of the cycle. By that point it doesn't interact with the detergent and I've found that it does rinse clean, leaving clothes smelling fresher than if I don't use it.
You can also use it as rinse aid in your dishwasher, although I've found you may need to increase how much "rinse aid" is dispensed for a similar effect. Still a huge savings over rinse aid. But I digress...
Folks have already explained that the fabric softener compartment gets added at the rinse cycle and is where vinegar should be added, but I wanted to add that if you'd like to remove fabric softener from your clothes or other fabric items, vinegar does a wonderful job and will make things absorbent again :)
I have always heard that using it too often is very acidic and bad for plastic and rubber seals on a washing machine. More so front load but also top load.
Even without fabric softener people should be running a hot water heavy duty cycle with bleach or washing machine cleaner every now and then because that sludgy buildup happens eventually either way
I've run 4 swlf clean cycles some with bleach, some with vinegar, and some with the professional washer cleaning stuff. It's still full of gunk. I'm pretty sure I'm just going to have to pull the drum and hand scrub at this point.