Musical Holding Tank!

Beware - this post mentions the T-word !

Whenever boaters congregate talk very soon tends to gravitate towards toilets. In this case I am reporting on our unusual musical holding tank that contains the toilet waste.

Albert has a shallow holding tank that extends across the width of the boat. On either side of the boat, in each gunwale, there are two connections - one for the pump out and the other for flushing with water. It is a very handy system. Originally the air vent for the system was one small hole on one of the flushing connections. This proved inadequate and caused unfortunate smells in cabin when the tank was partially full and the loo was used. In an effort to increase the ventilation to the tank and reduce the smell, I drilled 10-mm diameter holes in both flushing connectors. This dramatically reduced the odour problem but had an interesting side effect – the tank now plays tunes!

Shortly after drilling the holes we began to hear a quiet musical sound as we moved around the cabin. At first it  appeared to be coming from some distance away, but since we heard it at several moorings we realised that it emanated from our boat. Eventually we traced it to our holding tank vents. As the “contents” move around below the floor, air is forced out of the vents making a nice musical note. Both vents, being the same size, make the same note! Boaters mooring nearby are often mystified as to the source of the "pan-pipe" music and are often incredulous over our explanation.

Musical Holding Tank!
As the boat is rocked, sloshing of its "contents" causes air to play a tune in the vents

The video shows one of the vents and the boat being rocked to cause the air movement. I wonder what note it is playing.