I wouldn’t remove the case back. I’d remove the strap and toss the watch and strap into a tub with some warm water and Dawn dish soap. Let it soak for a bit and then clean it by hand.

If that doesn’t do it for you then you could go with a more extreme option.

 

I removed the case back on the solar to replace the "dead" battery before realizing it was silent 🤣. Tossed it in the window and it charged right up. Gasket looked fine. Still think it's safe to toss in water, having opened it?

 

The movement is easy to remove. Pull the case back. Stick the screws and gasket somewhere they won't get lost. The movement is held in place by plastic ring thing. It in circles the movement. Holds it in position.

The movement itself is a disc. Wear rubber gloves to prevent finger prints. Once the movement is out. Scrub the case however you like. Let dry. Use a computer duster...to dust. Stick it back together.

 

Any used watches I pick up off anywhere go through a pretty decent sanitizing cleanup which consists of:
1) remove band
2) remove bezel
3) fill a small tub with warm water, let the watch and its parts sit in it for 5 mins
4) apply some baby toothpaste onto a baby toothbrush and give the watch good brush
5) repeat 4) with parts if needed
6) rinse off, dry, & enjoy.

 

Similar to what's already been posted, but I'd stay away generally from dish soap. That stuff is quite powerful. Personally, I'd stick with hand soap. I've got an old toothbrush I use only for cleaning watches.

 

They use Dawn dish soap to clean wild animals caught up in oil spills. I don’t think it’s going to hurt a G-Shock.

 

In general, it's not necessary to remove the module (movement) to clean a G-Shock. This may cause more problems than it solves. If you do remove the module for some reason, don't lose the alarm spring or solar charging springs.

 

Unless you're really OCD, there's no need to go as far as removing caseback unless you feel gasket seals need to be refreshed with fresh silicone grease due to age.

In most cases of a used acquisition, what I do is to disassemble the watch, strap buckle and all, up to the watch case by itself. Module is well sealed within the case and grime doesn't make its way into there. However, that can't be said for watch extremities.

Then I soak just strap, bezel, and hardware in water with mild hand soap for an hour to loosen the accumulated gunk then go over hotspots/ problem areas prone to accumulation with soft toothbrush. Pat down with microfiber and then let fully air dry. Lastly recheck for missed areas and do spot cleaning with q-tip + soapy water. Same for module sans the soak.

 

I must add that those two actually look pretty clean for used G's.

To mirror nearly everyone above, you will have no need to take the modules out, unless someone has already been in and left prints in the inside of the crystal somehow!

By all means take the back off just to check there is a gasket in there before dunking them in water, I've received G's before that have had gaskets missing or damaged. Also then make sure all four screws are tight also.

Warm water, liquid soap and a toothbrush will be all you need to bring them back to how you want them.

Sent from my Pixel 6 using Tapatalk

 

Those pictures were taken after a pre cleaning with just a toothbrush and warm water. Believe me when I tell you the crevasses in the back were still gummed up with funk. I took all the advice though, and just removed the straps and soaked everything.

 

just take off the bezel and strap for cleaning ...
why would it get dirty inside the case?
think about it?
think about it?
really think about it?

lolz

 

you sound like you haven't taken off the bezel
remove the 4 screws (6 for the GD-100) and lift up the bezel which wraps around the button, search you tube if needed

 

I did now, ty! And it wasn't until today that i learned what a pain in the a** it is to reinstall these straps.

 

A regular cleaning involves just cleaning the strap and bezel and backside of the case and the crystal using just soap and running water and maybe a tooth brush and then wipe it dry with a soft towel. A thorough cleaning involves removal of the strap and bezel and then put the naked case and soak those parts in a soapy water bath for 15 minutes and then clean them with a tooth brush and then rinse under fresh water and wipe dry using a soft towel. A full deep clean is the same procedure with the bath but also involves removal of the case back to clean around the edges of the back case that can have some gunk build up and also some surface rust around the screw holes (common for watches that have been used in the sea) that can be brushed off with a tooth brush or finger nails.

Then next step is to clean the O-ring/gasket, usually this can be done with just your fingertips (make sure you have just cleaned your hands for this) just rotate the ring between your fingertips ( not very hard though, you do not want to stretch it out to much because that can destroy it) and it will get clean. Then clean the groove for the O-Ring using something like a wet cotton q-tip and tooth pick. Look really careful for all the dirt in that groove (requires a good strong light source like a flash light). Once you have cleaned all that out it is recommended just for the sake of it (since you are inside the watch at this point) to change battery to a new fresh one for battery operated non solar models then put some new watch silicone grease on that O-Ring and put it back in its groove and then close the case back (make sure you do not screw down one screw too tight before screwing down the other ones because that can cause uneven tension in the case that will increase the chance of stripping the screw holes or broken lugs).

Always screw down in a criss cross pattern and never overtighten the screws, once you feel the screw is all the way down just stop there no need to put a lot of torque on them screws. Then it is time to put back the bezel and straps and it is indeed deep cleaned. On older vintage models where some of the face plate might have degraded causing the crystal to fog up on the inside then a deep cleaning also involves cleaning those parts but that is not the case with your models.