Honestly, I have done a lot of pressure washing for houses and concrete before painting them, and The power of the power washer should be enough to wipe out anything. I power washed the concrete around a huge in ground pool, and it just takes time. If you need chemicals, ZEP makes good products for pressure washing. Also, maybe get a pump sprayer with an industrial de greaser. Zep also makes that and you can get it right at home depot. spray an area and let it set in for about 10 minutes and then pressure wash it. That should help a lot. I worked at a healthcare facility that had a brick patio. They gave us all day to do the job and one guy had spartan SD20 de greaser that is a foam type and you could have just hosed it down after he sprayed it with that stuff. it will take paint off walls. Good luck.