Exactly this. Use a syringe and inject hot (but not too hot) water into your ear with your head tilted. Do this a couple of times. Then you should use a paper tissue and your finger to get it out what you can. Repeat.

I dunno if this is a good advice, but it worked every time I got excessive build-up.

Some people just tilt their head to the right side in case it is their right ear and aim the shower head at their ear for some time. Sometimes it can just "fall out" (really, seen it happen!). Regardless, I just do the syringe one and paper tissue + finger.