I wanted a way to pick up waste when I was cleaning my tank. But I didn't want to buy a regular aqua vacuum cause they are battery powered and probably not strong enough. So I decided to use a Maxi-Jet powerhead (a lot of flow and corded, so more power).
At first, I used the top half of a water bottle connected to the MJ input and filled the neck with filter floss. Hand-holding the powerhead with the water bottle intake near the sand was powerful enough to pull detritus from the sand bed (avoided picking up sand by adjusting height from sandbed).
However, this was tiring and I had to be careful that the output of the MJ didn't blow frags off rocks or come shooting out of the tank, which is hard to do when you're concentrating on not sucking up all of your sandbed.
So for the next version, I decided to keep the MJ stationary using the triple suction cup mount, and move the filter intake. So I went by Lowes and found a threaded elbow that had a hose barb on the other end and a length of vinyl tubing that fit the fitting (I think its 1/2 inch).
I cut a water bottle in half and trimmed the edges so they were smooth. The bottle I used had ridges (I believe it was zeyphrhills brand).
Here are pics of the components.
click to enlarge
I cut a small hole in the bottom of the bottle that was just smaller than the diameter of the threaded elbow so that it would screw in and hold. The force of the suction kept it secure. The vinyl tubing went on the barbed side of the fitting and was secured with a ziptie (around the barbed portion) for good measure.
The mouth of the bottle fit snugly around the MJ standard filter attachment. I filled the bottle with filter floss and put the two halves together with some overlap, using the ridges to lock it.
Fully assembled.
click to enlarge
This assembly went into the tank vertically to displace the air from the tubing and floss. Then the MJ attachment went onto the powerhead. (Alternatively, you can put the attachment onto the powerhead first, then slip the mouth of the bottle onto the attachment, this prevents the attachment from accidentally being pushed inside the bottle.) Just make sure that the entire attachment is covered by the bottle so the powerhead isn't sucking in water from anywhere but through the filter. Also be sure to keep the vinyl tube in the water at all times, or it could suck air while on (and could siphon the tank when the pump is off). Point the output of the powerhead in a safe direction. The bottle might be compressed by the suction depending on how snug the two halves are connected.
And that's it. The velocity into the tube is very high, so keep it away from anything delicate (fish, soft corals, shrimp, etc) that you don't want to suck up. Also, keep it far enough from the sand bed so it just picks up detritus. It works great for vacuuming algae that you scrub off of live rock. Clears the water in no time.
When the floss is visibly dirty (or the vacuum suction decreases significantly), remove the whole assembly, drain (in the direction of filtration), remove and discard floss.
It helps to have someone helping to plug and unplug the powerhead in case you do suck up something delicate (Xenia are the worst).
You can also remove the tubing if you want to use the assembly as an additional in-tank filter.
Lastly, feel free to modify to fit your own needs. It only cost me less than $2 for all the parts (I had a spare MJ).