I dilute it 50/50 with tap water and soak what I can. Home depot sells two strengths. Full strength is usually kept with their outdoor garden supply stuff which might need to be diluted even further. I have only used the "eco friendly" stuff which is weaker but it works great and is usually with some of the paint supply stuff. I soak pumps, skimmers, and anything else that needs a good bath for like 10 minutes then rinse. Comes out super clean with almost no rubbing or scraping at all.
you could spray it too but be careful doing that make sure you are well protected it will eat through concrete and other stuff and does some weird stuff to aluminum and other metals but I have not had any issues with plastics, acrylic, or silicone.