I got a backwater valve installed in my basement. The water table was high, so I could not use a backwater valve with a see-through cover; I had to use a valve that is typically used for outside installations. I can access the valve for maintenance through a 6" wide PVC pipe (see picture).
With the see-through backwater valve, one can easily see if there is a backflow situation. There are also some alarms that can be used to warn of backflow situation. However, with the current setup I can't see if there is a backflow situation without opening the 6" cap. This could be a bad idea if sewage starts spilling out of the open pipe. So I am thinking that it would be great if the cap was transparent. I couldn't find such a cap googling around. Is there such a thing as a transparent 6" screw on cap?
What tool does one use to open & close these caps anyway? It is a 2" counter sunk square.
Also, since it seems that off the shelf alarms don't exist for these 6" cap, I was thinking of making my own with an off-the-shelf water alarm combined with the cap. I would have to drill some hole(s) through the cap (transparent or not) and feed the wire through. The plate would go inside the pipe and the alarm outside. How would I seal the hole around the wire? It would have to be airtight, and strong enough to resist a backflow pushing up against it.