The tank drain is separate from the pump and shouldn't have any drainage with the pump on. The drain is just a hole in the bottom of the tank with a valve attached. If the pump is on, drain closed, and you're still getting water under the coach you have a leak somewhere. Open all your basement doors, turn the pump on and start inspecting with a flashlight, the water could be coming from anywhere there is a fitting or joint.
Dave & Myra
One day your life will flash before your eyes,
make sure it's worth watching!