Water Presure

[muddflapp]

We have a 2008 3400 Monty. When we are running the water in the kitchen sink, we have very low presure. While running the water, we go and flush the toilet and the presure increases. The water stays at a higher presure until we turn the kitchen faucets off...Why is this happening and how can I get higher presure without having to flush the toilet to get the higher presure?