Would this work?
Raise the bed, block the bed and fill full.
Then put a pipe nipple in the fill hole with tygon tubing attached that goes back to a bucket.
Lower the bed slowly while monitoring the bucket.
Raise and lower the bed several times making sure the hose is out of the fluid and does not suck fluid back into the cylinder.
This should contain most of the mess and bleed the cylinder.
Then raise and block, remove nipple and reinstall the plug.

There are a lot of ways to do this and this is a way I would consider.
And I can't stress this enough,
MAKE SURE YOU OVER BLOCK THE BED FOR SAFETY!!
2-Ton


1967 GMC 9500 Fire Ladder Truck
"The Flag Pole"
In the Stovebolt Gallery
1946 2-Ton grain truck
1946 3/4-ton pickup,
1953 1-ton pickup
1957 1-ton flatbed dually,
1954 Pontiac Straight Eight
Of all the things I've lost in my life, I miss my mind the most!