Rinsing your pump benefits the hose and the hose reel more than the pump. I rinse after every use,...you need to refill for the next job anyhow,...so just cycle approximately 10 gallons clean water through your plumbing back into the mix tank.
I did not rinse my all flo until it hit 100 roofs. I figured that was a sufficient test. Try that with a Delevan..Hah! But like jeff said your hose and reel need rinsed anyway.
if you are using a PVDF pump with Santoprene elastomers you really have no real need to run fresh water through the pump. It would be a good idea if your are not going to use the pump for weeks to fluch out with fresh water
What Steve says is true, but what we have found is this. When chlorine dries out, salt crystals remain that can interfere with pump operation, sometimes. But it is true, Kynar and Santroprene laugh at Chlorine, the hose reel manifolds and swivels suffer more.
Our pumps get rinsed out at the end of the last roof cleaning job for that day, so if we do just one it gets flush after use, if we do multiple roofs back to back we just do it on the last job. I have had the same yamada kynar pump for over 2 years now and still going strong.