Freezeproofing a Garage Sink
Frostproof valves and a P-trap make for a functional slop sink in this garage workshop.
Every shop needs a slop sink, so I decided to install one in my attached garage workshop. Because I live in a cold climate and wanted to use the sink year-round, frost protection was mandatory. My solution was to locate a plastic laundry sink on the wall shared with the house and to use frostproof sill cocks for the hot and cold water supplies. These valves are normally used for outdoor faucets and are available in both 8-in. and 12-in. lengths. The supplies run up from the basement inside the shared wall, protected from the cold by the warm interior of the house and its insulation.
The tailpiece from the sink’s drain takes a 90° turn by way of a 1-1/2-in. horizontal PVC drainpipe, which penetrates the rim joist before joining a P-trap in the basement. Putting the P-trap in the basement keeps its contents from freezing.
Whether it be for washing paintbrushes or just for scrubbing my dirty hands, the slop sink has been a satisfying addition to the workshop.
Karl Juul, Glenmont, NY
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The only hiccup I see here is the trap for the sink. From the drawing it looks like it is under the floor. Is it accessible from below? If so, you've got the perfect solution. If not, there is a potential problem if it develops a clog.
If it is an unfinished basement, there is no problem. I put in a sink with a drain like that nearly 20 years ago an no problems yet. If I do have problems, it will require a trip into a nasty crawlspace.
I wish I would have though of the frostproof sill cocks. I used conventional plumbing that I turn off and drain every winter. Where I put the sink doesn't line up with the utility room where I tap into the plumbing so to change it, I would have to move the sink and the drain line.
The 1.5" drain line will need a vent installed shortly (less than 3.5') after the trap. Otherwise flushing a toilet or other fast-flowing drain may suck that trap dry and you will have an awful smelling garage. Size of the pipe determines the length from trap to vent.