1998 Honda accord Fuel gauge doesn't work?

1998 Honda accord Fuel gauge doesn't work?

Added (1). 1998 Honda Accord Fuel Gauge doesn't work, Please help!

I recently bought a 1998 Honda Accord EX V4 2.3L from a private seller and besides being old, it works great. However I noticed that the fuel gauge doesn't work properly. I filled the gas tank and within 4 days (With few miles driven) the gauged went down to empty. The Fuel Tank light hasn't turned on so I assume it still has gas in it. I've looked up YouTube tutorials on how to change the "Fuel Tank Sending Unit"

and my questions are,

"Can I check the sending unit while the car is on?"
"What do you recommend I do? Get a mechanic or fix it myself?"

There's another video on youtube, don't know how you've missed it because it's right below the video that you've listed above:

Yes, you can check the fuel sending unit with a DVOM (Digital Volt Ohm Meter) but the whole fuel pump has to come off: Access the fuel pump from the trunk (See the video)
Measure the resistance between the No. 1 and No. 2 terminals with the float at E (EMPTY), 1/2 (HALF FULL), and F (FULL) positions.
If you do not get the following readings, replace the fuel gauge sending unit: At Empty (105-107 ohms), at Full (3-5 ohms) and at Half (29-35 ohms)1998 Honda accord Fuel gauge doesn t work - 1