Maybe be a dump question here.
I read on a post where someone had used somewhere around 150 gals of bleach to do a SLAM (don't know what % the bleach was).
I suppose not knowing in advance how much you would need doing a SLAM, every situation would be much different, but I wonder why I don't read of anyone doing a water drain of whatever before doing a SLAM.
I estimated my cost of draining 7500 gals of water and my cost would be around $75 which would be about 20 gals of 12.5% bleach.
If I think I would be using well over 20 gals of bleach would I be better off starting with draining some water first?