I feel for you, I had two water screamers.
Goggles worked with one, the other absolutely hated them (so do I)
A couple of flannels on standy by, all folded up and one placed over their eyes - my screamer would get worse if the flannels got too wet
Encouraging them to lie down in the water to rinse the hair in the bath water to get rid of as much water as possible, then the final rinse with clean water isn't as hard on the eardrums.
Leaning the head back and slowly pouring the water over their head. With one it was the feeling of the shower
There is also a weird hat/ring thing that goes around their heads to prevent the water going into the eyes/ears/down the face.
If it's an ear thing, reusable ear protectors.
The chemical stuff isn't worth it.
Conditioner with tea tree is the best.
If rife the zappers can be useful to zap loads in one go. However, ime you still need to use another method.
Don't forget to wash towels, clothes worn while combing and bedding. Recomb every 2/3 days. The. beauty of the conditioner is from the second time you find you don't use as much and is fine as a leave in conditioner.
Yes I know, rinsing hair in bath water and leaving in conditioner for a day or two is a bit grim, but when it's really distressing them out what can you do?