No way to do it with just a can tapper.

With hoses and a set manifold guages, it works as follows. Close both hi & low valves. Attach both hi & low side hoses. Crack open the low side valve, allowing a slow flow of refrigerant up the low side hose, into the manifold, and down the charging hose to the can tapper. After a few seconds of allowing the refrigerant flow to push the air out of the hoses, tap the can.

There are other procedures as well.

Can't do this with your setup because you don't have a shutoff valve to control refrigerant flow though the hose.

- JimY