See the three parachutes? The bottom one is titled Boiler and Central Heating, with a spanner. In the middle is Plumbing, with a plunger. At the top is Drains, with a Stilsons wrench.
Now would you fix a drain with a Stilsons wrench? Wouldn't you use a plunger to unblock it? And what would you use a Stilsons pipe wrench for, if not the pipes in your plumbing?
Get it, now?