1999 Ford Taurus Submersible fuel pumps/lines

Hey everybody. I've installed a submersible fuel pump in my 1999 ford Taurus LX with single overhead cam engine. The pump works great, but the lines I have installed inside the tank keep coming loose or ripping when left for a day or two. They are simple soft rubber lines from O'reilly auto parts. They are a replacement for the old plastic corrugated lines. The man said they were submersible but I really don't think they are. Can someone please tell me what type of hose would be best to use inside of the gas tank to connect the submersible fuel pump to the fuel system. My car simply won't run because after being driven for a few miles the lines come lose inside of the tank and the car does not get any fuel. Once the lines are reconnected it runs great. I've done that twice and I've determined that the current line isn't working. Thanks so much.