Water got into my Hella 450s when I drove through some water. It got in through the back where the bulb goes into the housing.

I removed the reflective housing but it's one piece with the glass. I only have access through the hole where the bulb goes in.

Obviously I shook out the water, but how can I clean out and residue that might from on the inside of the glass?

I've checked the internet, either people leave them out to dry or pop the glass out. Could I pour IPA in it, shake it around then dump it out or would it ruin the inside?

Figured it out already.

1.Shake out the water as best as you can, add high % alcohol and shake that around and drain it. Then take a low lint paper towel or micro fiber cloth and put it inside the housing (a smallish wod). Take a Q-tip and use it to push the cloth around the inside.

2.If there is still some residual spots of liquid use the q-tip to dab them up. Remember you can bend the q-tip to get around the center of the light reflector if you need to.

3.There will likely be some dust but as long as its not too bad it wont affect much. If you have Rodico you can use it to pick up the dust, but I don't have any Rodico.

4. I've been making it up as I go. If you want the dust gone take a new micro fiber cloth (like comes with glasses), fold it and then push it into the light. Shake it around, use your pinky finger to apply pressure to the cloth if you can. Then pull the cloth out. I'm pleased with the results now

You've outlined a good method for cleaning out the inside of the Hella 450s headlight housing. The key is to use a high percentage alcohol, such as isopropyl alcohol (IPA), to break down and remove any residue or water spots, then use a low-lint cloth or Q-tip to wipe the inside of the housing. You can also use a microfiber cloth to remove any dust inside the housing. Remember to take safety precautions such as disconnecting the battery before cleaning the headlight.