Many of you may know that we lost a hive to Argentine ants last year. We tried many things to control them, including borax-laced syrup (failed) and then my first home made ant moats. The problem we had with the first ant moats is that the ants were willing to drown enough of themselves to bridge the moat, then they built a nest in our SBB which prospered while we were on vacation. Having learned from that, we have a new design with a much wider moat.
The moats are made with PVC drain caps. A PVC end cap serves as an “umbrella” over the moat, to keep out leaves and rain etc. The center support of the moat is a simple canning jar. Using a lid allows the lid to be unscrewed from the moat, vastly simplifying cleaning and refilling. Photos of the concept follow below. 
Shopping List
- PVC drain caps 4" diameter. We used these:
http://tinyurl.com/lnks5yd - Half cup canning jars. We used these:
http://tinyurl.com/lqk5d7j - Plastic canning jar lids like these:
http://tinyurl.com/n89zvmx - PVC end caps 4" diameter. These work well:
http://tinyurl.com/lo9hxjl - Epoxy glue, like this:
http://tinyurl.com/lgerj3b - Mineral oil - we just bought some pharmacy grade from our local grocery store.
I suggest you make at least 5 moats at once. Then if you have one under each corner of the hive, you can use the fifth to swap in while you clean out a dirty one, and you don’t have to lift the hive. Just ease it under the edge. Here is a layout of the parts needed for 4 moats:
Method
The first thing I did was cut 15mm (~5/8") from the rim of the deeper drain cap, so that the ants could not reach up to the covering cap.
I then glued the plastic canning lid to the center of the drain cap, using lots of epoxy on top of the canning lid.
I let the glue set, and screwed the canning jar into it. Then I smothered the upturned base of the jar with more epoxy:
Finally I put the end cap on top of the other 3 parts and weighed it down with a heavy book for a few hours. The final ant moat looks like this:
Two days later it was put into service. I just unscrewed the lid and dribbled Mineral oil into the drain cap, almost up to the top of the canning lid. I screwed the jar back in, and slid the moat under the hive.
Two weeks later it seems to be working well. We are ant free. There were one or two dead bees in the moat, but with the unscrewing lid, it was easy to remove them with some tweezers.
Hope somebody else finds this useful. 
