Ideally you want a lighter touch than that so you don't provoke that reaction of them expelling water from their body cavity to clean off their disc. Larger anemone will survive a treatment after doing this. The lighter touch is harder to do than say, but if you have a good angle on the anemone it's very possible and definitely more effective. (Sometimes the angle dictates you just have to shoot it at them and pray.)
Any time they get buried in sediment, this would be their response to self-clean. Not an uncommon response from any polyp-based animal. I suppose there could be reproductive members in the jet of water, but I don't know if there would always be. Seems like that would make self-cleaning a very expensive behavior ecologically speaking.