Fuel pump replacement, water leak

1) change engine and oil filter BEFORE you fire it up. Oil filters that have sat in old oil for a while can fall apart. Plus the oil is possibly garbage as well. No need to push bad stuff thru the system. Oil and filter is cheap... engines are not.
2) tighten all the water pump housing bolts / alternator bracket bolts BEFORE you replace coolant... had antifreeze leak from block to timing chain cover before internally and ended up with coolant in oil from loose bolts.
3) I’ve filled my coolant system with Cola-cola before. It’s a type of mild acid. Cleaned out a lot of rust and junk before I popped the freeze plugs. Made cleaning system a lot easier.
Cleaned the radiator inside too.
I only leave over night (8-10hrs)as the acid in the soda will eat thru the copper radiator core if it is thin.

Good luck.