When a slip-lock fitting is used, the tubing must make it past the lock and o-ring that prevents any water leakage. For our mist slip-lock fittings, this means getting the tube in to a depth of 3/4″. It is common to discretely mark this spot on the tubing to ensure it makes it in all the way. Below is a picture of a properly fitted tube. The dark circles mark the internal o-ring. You may need to twist and push the tubing to ensure it makes it past this o-ring for a leak-free connection.
To remove a slip-lock connector and reinsert it, press the tubing and end of the connector inwards. Then, holding the connector in place, tug the tubing free. Examine the end of the tubing before reinsertion. If it is pitted, crimped, or creased, it may be a good idea to snip the end for a better seal on reinsertion.