I always thumped that tanks for the start of each chemical and inverted the tank at the start several times and then several times again every 30 seconds when I used steel tanks.
Did some testing this weekend and concluded inversion agitation is the way to go.
I also found that Paterson Super System 4 tanks do not leak. The key is putting the lid on properly, and my wife showed me how it’s done when she pointed out that it’s just like putting the lid on a Tupperware container.
Rather than pushing down on the edges of the lid all around its circumference, the right way is to set the lid centered on the tank and then push down in the middle of the lid with the heel of your palm. You’ll hear some air escaping from the tank, and this creates a slight vacuum in the tank that will hold the lid on. Viola! No leaks!