Hi,

We are on tank supply, and a few yearas back we added a 10,000L tank to our system (already have a 20,000L tank).

They are connected together with a thick alkathene pipe via their outlets at the bottom of the tanks, and a t-junction goes from this pipe to the pump under the house to supply water for the house. Both tanks have a tap into this pipe, and on the pipe leading to the house off the T-junction, there is a non-return valve.

Generally, we draw water from the original tank, and leave the 10,000L tank turned off once full (in case we have a leak, or a tap is left on - it does not use all the water, and we use the water from the 20,000L tank as that is where the rain water goes (guttering only goes to the big tank).

Problem is, when we switch over to use the smaller tank, we get air bubbles in our water system. For the most part it works fine, but sometimes when turning on a tap it spits and bursts a bit till it evens out, but you can hear air in the system. It does not do this when drawing water form the main tank, only when the main tank tap is off, and the supplementary tank is on (if both on, it is OK, and the levels of both tanks comes down equally, as it should).

Plumbers, or other enlightened people - any idea how this air is getting into the system and how to stop it?

The bottoms of both tanks is about the same level, both tanks have access for air at the top.