To start this, you will need 2 bottles (any size) as long as the caps fit, glue of some kind, and a knife.
I did this as I am currently a truck driver and occasionally buy a gallon of a liquid but only want a small amount of it at any one time. Could also come in handy if you have children in the home and want portion control to.
Step 1: Cutting the Lids
simply cut the center out leaving the inner ring intact so you have a hole in the center and an edge to glue the second cap to.
Step 2: Gluing the Caps.
glue the caps together as shown so you have a through hole to the bottom bottle
Step 3: Cutting the Bottom of the Transfer Bottle
cut the bottom off the second bottle to make a funnel
Step 4: Assemble
Put the bottles together and transfer your liquids. very handy if you need to transfer from a gallon of whatever to smaller bottles.