Replacing Radiator, should I replace it THEN do an engine radiator flush

Or do a radiator/engine flush first THEN put on the new radiator. It sounds silly I'm sure, but I don't have access to a water hose. I'm doing this parked on the side of the road. So to clean my entire engine I bought Prestone rad flush + cleaner. Seems like doing the flush with the old radiator will do two things, clean the engine inside of rust and what not, and should the old rad spring some leaks, no problem as I'll be replacing it right away. Sounds like a good plan? Kinda low on options, except, perhaps...try to use the hose at local car wash lol