keep on wringing / keep on squeezing

keep on squeezing / keep on pressing

keep on straining *one's voice

keep on striving hard to think out [a plan] / keep on straining *one's wits / be trying hard to squeeze out [an idea]

keep on extorting money from *someone / keep on squeezing money from *someone

keep on reprimanding *someone

keep on drilling *someone / keep on training *someone hard

keep on stopping down the lens

keep on turning down the volume

keep on drawing a bow hard