What Doc said. Fuel pump. Plus...
Modify the lid (or A lid) for one of those fancy fuel fittings; fuel line with bronze filter clunk inside the 5gal can.
If you’re going to mix a lot: Electric (Boxxer?) pump on the outside.
If you’re not going to mix a ton, or if you want more precise control: Six-shooter manual pump.
Fold up a rag / shop towel and put it under the back edge of the can to tilt the can forward.
When the can gets lighter shake it to make sure the clunk is in the deep spot under the cap.
Another possibility would be to modify a cap by adding a small brass spigot and as Jerry suggested, lay the can on it’s side, and let gravity do the “heavy lifting”.
PW