A good Idea, but requires attention to what's in the bilge.
Uncles sailboat was rigged this way, and developed a leak along the shaft that was beyond the capacity of the electric pump (something broke and the shaft and prop departed the boat). There was about two feet of water on the sole. Activate the three way valve, and started pumping, sucked in lots of water. Sucked carpet scraps, paper and stuff on the sole up real fast and blocked the strainer (a big one with 1/2 inch holes).
Cooling water to the engine was restricted, and the engine overheated (according to uncle took about 5 minutes). Because of the bilge alarm, the engine noise, and distractions with the radio and stuff, didn't hear the engine alarm and didn't detect the problem right away. Luckily the costies got there with a BIG pump. Engine was fried.