Have a second output is very useful. If he is at the top, then the air goes into the canister freely. Liquid spill, and quiet flows the stream. If you make the output at the bottom, it is convenient to connect the hose. You can use the canister as a watering can. You can put it high and wash the car. You can hang on the tree. And so on. The easiest way to use a metal barrel fitting and cork. But you can take the neck of the bottle. It is very cheap.
Step 1: Preparation.
We drill a hole in the canister where we want to, above or below. Cut off from the neck of the bottle. It should be larger than the hole and not to fall.
The neck mounted inside the container. It will cuddle up pressure. To deliver the neck inside, use the wire. We pass the wire through the hole. Emphasis, that would not come off the neck. Pull the wire and pull the throat to the hole.
Use thermal glue to seal it. When cool - can use. Cannot be stored in a canister of petrol and oil! They destroy the thermal glue.
Sorry, it's a machine translation. But all is clear from the pictures ;)