A friend brought me the coolant tank (reservoir) off of his Arctic Cat F6 Sno Pro. One of the small plastic nipples for a hose was broken off. The red arrows point to the nipple and the location that it is supposed to be connected. A new tank is probably not to expensive, but would take several weeks to get here.
The plastic that these things are made from seems to be impossible to glue. Luckily the area on the tank where the nipple was located was thick. I decided to drill out the old hole and tap threads for a new brass fitting. When tapping threads you must be sure to use the correct size bit, normally the size is printed on the side of the tap. In this case I am tapping for a 1/8" pipe thread and the correct drill is 21/64.
Make sure that the tap gets started straight in the hole. Pipe threads are tapered, don't run the tap in too far or the hole will end up oversize. Stop and check the fit often. A good rule of thumb is - 3 loose, 3 tight, 3 showing. This means that you should be able to turn the fitting in three turns by hand, three turns with a wrench, and have three threads still showing when finished.
I applied a little bit of Leak Lock to the threads before assembling the parts. Most standard water plumbing thread compounds are Teflon based and are not supposed to be used with petroleum products. On anything involving oil or gas I use Leak Lock.
Here is the finished repair, a $3.00 brass fitting and 15 minutes.