What I do to get rid of aphids is the following...
1. When it's time to water the plant (I water daily), wrap the pot and soil in Saran Wrap.
2. Add rubber bands so the wrap stays tight around the pot.
3. Fill a bucket large enough to hold the tree, with tepid water (not too cold, not too hot), then add a tablespoon of dish detergent, mix gently and try not to make too many bubbles.
4. Lower the tree, upside down into the pot until all of the foliage and branches are under water and lightly move the tree around in the water.
5. Take the tree completely out of the soap solution for a few seconds, then repeat.
6. Place the tree somewhere to "dry" for a few minutes.
7. Unwrap the pot and water the tree and foliage thoroughly to remove the soap and dead aphids. Don't forget the undersides of the leaves. You can even do a second bucket of just tepid water for rinsing the foliage.
8. Repeat the process in 1 week, for 2 weeks (3 treatments in 3 weeks).
9. Enjoy your aphid free trees.
This is a bit tedious, but not as tedious as removing all of the aphid-damaged yellow leaves from your trees everyday.