toilet help needed

I replaced my Thetford toilet with a Dometic 310 toilet in my Tahoe toy hauler. The replacement went smooth and easy. My problem is when you flush the toilet and then don't use it for a few minutes it takes about 3 seconds for the water to reach the bowl. Sometimes it takes longer if it sits. I talked to customer service and we went through a few steps. First we hooked it up to the city water connection, still did it. I was sent 2 screws to secure the water valve(some toilets were being sent out without those screws), No result. Then I was sent a new water valve, no result. Dometic is going to send me a replacement toilet(awesome customer service). My problem is I am afraid it is going to do it again but I cannot think of what the problem on the trailer side could be. The old toilet did not do it, I replaced it because of a broken pedal. Any thoughts or suggestions are greatly appreciated. Thanks