I use 1/2 - one pound casts or compost in 5 galllons. So 8oz is two cups for half pound by volume. 4 cups for a pound of casts? But check I dont measure in cups.
In 5 gallons I just add and stir it well. Larger volumes, 50+ gallons, and using sump pumps i put it in a tea bag(s). Then steep it with hand agitation to extract the microbes, nutrients and fine sized compost particles. And sometimes the sump pump goes in a tea bag too. Such as for 300+ gallons extract and not enough tea bags to hold the casts, where I just mix it in the stock tank. The fines can bind an impeller.
You dont dilute it use full strength, and use soon then top dress the used casts if you want.
Thats more the extract method I currently use. Its incredible. 5 gallons of tea should feed the two plants well.