I have a 1970 Chevrolet Corvette with air conditioning.
Like all owners of these vehicles, I find the location bag to hold the windshield washer fluid awkward, particularly trying to refill the bag.
So I've come up with a solution, not perfect, but here goes:

This system uses mostly existing tubing, and fills from a 20 ounce pop/soda bottle.

1) Get some extra washer hose tubing.
Here's a Corvette specific source: https://www.zip-corvette.com/69-72-w-ac-windshield-washer-hose-set.html
Here's a generic set from Amazon which includes some Tee connectors: https://www.amazon.com/Windshield-Washer-Hose-Kit-Installation/dp/B0BMFPMK6R/ref=asc_df_B0BMFPMK6R/?tag=hyprod-20&linkCode=df0&hvadid=693697547933&hvpos=&hvnetw=g&hvrand=13065723805735384139&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9021887&hvtargid=pla-1946662448624&psc=1&mcid=6463f5f10bbf3e2e9208092cc28d541d

2) Print the three parts in this thing (unless you bought the hose set that includes a Tee connector). You may want to print the plug at 98% size for an easier fit. Unless your engine bay gets unbelievably hot, PLA will work. I have a red car, so I used red PLA.

3) Cut the washer hose between the bag and the pump. See pictures for where I chose. Insert the cut ends of the hose onto the straight parts of the Tee.

4) Cut enough of the new hose so you can attach one end to the Tee connector, and have enough length to attach the hose with the spout onto a 20 oz beverage bottle. Attach one end of the new hose to the Tee, and one to the spout.

5) Secure all connections with zip ties.

6) After printing the plug, either glue a rubber disc, such as a furniture foot pad (which is what I used) , or a printed disc made of TPU, to the top of the plug.

Here are some pads from Ace Hardware that fit the application: https://www.acehardware.com/departments/home-and-decor/furniture/protective-furniture-pads/5089586?x429=true&gad_source=1&gclid=CjwKCAjwuMC2BhA7EiwAmJKRrNSGDXXLEZehXfbi_83brP2V62OVsZvQr-4ilCTSPJCw-asY_iYHrBoCJJsQAvD_BwE&gclsrc=aw.ds

I hanged (hung?) the tubing from an existing bendable cable holder on the inner/under side of the fender. When I want to fill the bag, I take out the hose out of the cable holder, take out the plug, screw the spout onto a bottle I've filled with washer fluid, turn the bottle upside-down, and gently squeeze. When done, unscrew the spout, screw in the plug, replace the hose.

Please feel free to comment, remix, improve, etc.
No donations/tips needed or accepted; just don't sell these or use the design to make any kind of profit.