Normally I would copy and paste the entire Reddit post here but the author has politely asked people not to and I’m not a jerk so the link is provided and it’s also here.

Laundry spa day is essentially a reset for your clothing using enzymes. Here’s an additional Reddit Post called what is spa day?.

Essentially, you’re trying to get your clothes back to a state with little to no soil, oils, and grime. You’ll do this by using different enzymes and cleaners (don’t mix and match without knowing your chemistry!) in a bucket/bin/tote of hot water and letting your clothes soak in it.

There’s plenty of information within that post, I don’t want to essentially re-write it or it defeats the purpose of the author’s request.