I purchased a Watchman Alarm a few days ago to fit to my oil tank.

My oil tank already has a pre-drilled hole with a sticker besides it
saying 'Watchman Alarm' - unfortunately the hole is only 25mm wide so I
would need to purchase a suitable 32mm hole-saw and make it larger.

That's not a major problem, what concerns me is that the part of the
tank where the pre-drilled hole is located is on a very slight curve
(if I rest a level ruler on that surface that's the diameter of the
alarm then the ruler has about a 1mm or 2mm gap under each far edge of
the alarm diameter). This would cause a problem fitting the washer and
the alarm - if the base is screwed down tight then the lower part of
the alarm fitting will bent slightly and the main alarm unit won't
screw in correctly (I haven't tried this, I'm basing this on
assumption).

The only suitable flat surface that I can see is the large 'bulges'
that can be seen on most tanks - the plastic 'ribbing' if you like. The
trouble is that these are higher than the fill point (not 'allowed'
according to the Watchman instructions) and, due to their height, I'm
not sure if the signal from the detector will reach into the tank
correctly.

What can I do, if anything?


Thanks

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