with regard to using white spirit/meths and a toothpaste?

whats the technique, is it as simple as scrubbing the aphids off the leaves with a toothbrush thats been dipped in meths? what about the fluid that drips onto ground/borders, will it do much damage?

as my plum tree is badly infested and the organic solutions don't really seem to have done much. i believe the tree is suffering aphid leave curl and may have for a few years as garden was overgrown mess when bought last October.