May need to prime the water pump, just have another bucket of clean water and insert the siphon hose into it and let the pump run for a couple minutes. Don't run the pump dry too long or might burn up the water pump. I have a GH 31ss, and I believe there are two different settings on my main water manifold, one to fill the water tank and one to sanitize/winterize. May need to change the manifold setting as well.
'08 Greyhawk 31SS