I like a good quality washing up liquid. To get the best deal means buying larger bottles. My wife prefers the smaller size to use so I regularly top it up from a bigger bottle. how ever being more viscous than the cheaper brands a good couple of washes worth sticks in the bottle to get as much as I can from each bottle I made a double top that lets the almost empty bottle drain into a new one this gets almost the last dregs from the bottle without resorting to dilution.
Step 1: Materials
2 clean bottle tops and the ubiquitous hot melt glue. luckily the brand I like uses screw tops which are the same regardless of the size of bottle they are on. They need to be clean for the glue to stick. I took 2 off bottles that hadn't been used, but it's washing up liquid it comes off easily with water.
Step 2: Trim
with your knife of choice trim the sealing cap off at the hinge. also trim the flared out tip off one of the nozzles so that it's a smooth taper
Step 3: Bore the Receiving Cap
the nozzle of the untrimmed cap needs opening out until it is a snug fit on the trimmed one. using just the chuck from my drill as a bit holder and set of drill bits that increased in 0.5mm steps I started with the next one up from the size of the bore and opened the bore up 0.5mm at a time holding the chuck still and twisting the cap by hand until bore was a good fit on the trimmed nozzle of the other cap.
Step 4: Glue Together
I trimmed away the outer wall of the nozzle so I could push hot melt glue into the void between the inner and outer nozzles when they were pressed together. I also filled the groove between the 2 wider threaded sections with hot melt glue for additional rigidity. I'm not the greatest fan of hot melt glue there are frequently better glues for most jobs but for sticking plastic to plastic and forming large fillets it's pretty good.
Step 5: In Use
fit the bored cap to the recipient bottle tilt the assembly over and screw the bottle being emptied into the other cap. As the liquid will run to the side of the bottle it saves any loss from just inverting the bottle being emptied. the two can now be left to stand for a couple of hours if or even over night. not every drop is recovered a little still collects on the lip below the neck