Got you pumps set high haven't you?
I have mine at the bottom of my tank, water is gravity feed to then so reducing the chance of airlocks. When water gets below the the pumps this could drop the level in the hose leading to the pump, especially if you clean the filters out, you will get lot of air into the pipe that you will have to pump through,
That won't run air locks out as that's below the pumps. If it's anything like why I have a tap on mine like that it will be to either empty tank when needed to and to top up barrels or backpack.
Good Lord Spruce! A veritable work of art and symmetry!
Yer I know when my van went in for mot they told me I had to empty tanks for them. Plus if anything goes wrong with van, you can empty it with ease so you could move it.