Hi, since you are talking about bumping the handle I believe you probably have the EC series hayward filter. I have the EC 40 model with the bump handle. It is my understanding that the handle is supposed to release the de from the fingers and then allow it to recoat, extending the time till you need to backwash and add more De. When you backwash you are removing the de from the filter and it must be replaced. Not all the de washes out but I always add the required amount anyway (mine uses 4 lb. of de). The extra just seems to stick at the top of the filter and does not seem to do any harm. At least once a season I will take the whole thing apart and give it a good cleaning with the garden hose. I also do this at the end of the season so that I am putting away a clean filter. I know there are a lot of bolts to undo and it is a pain but it keeps the filter working without problems.
Ken