[Richard]

Is it leaking from the barb where the tubing connects to the elbow?

Or is it leaking from where the elbow connects to the pump?

If leaking at the tubing connection, snip off 1/2 inch of the tubing and try again. The vinyl tubing can take a “set” over time and may not be very tight on the barb.

If leaking at the elbow to pump connection. Clean the connection first. Look carefully to see if the stiff tubing is cocking the connection. I had to use a long piece of tubing and bend it in a complete loop to get the tubing to align properly without putting a sideways force on the connection.