I bought a $18 12V Scavenge pump.
Your HWH has a few relays with 12V power right next to the reservoir. However, if you don't feel comfortable using that power source, then just pull you car up and tap into your car's battery for power.
https://www.amazon.com/ATPTOOL12V-Ex...NsaWNrPXRydWU=
This works great, but you will find the fluid in the hose can be messy. So have a few plastic bags ready to go. Then I used the scavenge pump to replace 10 quarts in my hydraulic steering and fan clutch reservoir back by my ISC-350 engine.
Note: If your fluid is 10+years old, I would change it. And don't use just any Dexron III. You want to avoid the types with additives or if they say "For High Mileage Vehicles." Also, the cheap stuff is fine if you can find it at Walmart, but not always. I had to go to Napa and pay $6/quart.
If you are just trying to top it off, maybe you can roll up a piece of printer paper and make it into a funnel.