Drain Main Water Tank

[jmj437]

I have a 2004 GS BT Cruiser 27 foot that I recently purchased. How do I or is there a way to drain the main water tank under the rear bed without having to use the pump and turning on the sink/ shower or flushing the toilet to drain the tank? Is there a drain cock of some type in or around the tank under the bed to drain it.

There must be a easier way to accomplish this task.....................

Thanks in advance.