Formula changed the design on the 400 in 2002-2003 and eliminated the deck fill option. basically you have a check valve solenoid that is routed through to the water tank. In the cabin there is a switch to allow the system to by pass the water tank and run off city pressure, or allow the tank to fill through the solenoid valve, or run of the water pump. On my 2003, I drain all the water out of the tank running all faucets. I then drain the hot water tank. I have installed a bypass valve system so that I can by pass the hot watertank.I then disconnet the quick fit connector at the pump. If you look at the set up, you can trace the flow past the valve to where the tube enters the tank. That can be disconneted and antifreeze can be added to the tank. I then attach an extension tube to the pump, prime the pump and have the tube inserted into a 5 gallon bucket of antifreeze. From there, simply turn on each faucet one at a time, for both hot and cold and run the water pump. As I said, I have bypassed the hot water tank, so there is no need to have it filled. To be honest, the water tank is aluminum, and if completely emptied would not have enough water in it to crack it. I am in Michigan and have not had a problem with water in the water tank. I have yet to add antifreeze to it.

After looking at it earlier, I basically came up with this as well. I couldnt figure a way to bypass the water tank without extra push connectors and hoses.... That will be on the project list next year.

I appreciate all the info and help from everyone!!

Happy thanksgiving

I can give you the part numbers and pix of the kit i used if you like. Only tricky part is that the kit is standard id, and the hoses and fittings formula uses are metric. pm if intrested.