A lot depends on your style of camping. If you're mostly in electric hookup campgrounds or only out of week-ends for a couple of day, do which ever you like, it won't matter much.
If on the other hand you expect to be in places without electricity for more than a day or two a manual might serve you better. Remember that electric pump uses battery
power. The more battery
usage the faster you run out of battery
We're never connected to electricity therefore the manual works just fine.
FYI-- we extend the usage of the water in fresh water tank by using pot to collect water for coffee from the local spigit the same as you did without the water system.
Don't forget that the drain water has to go someplace other than the ground. Therefore I think it would be wise to add a gray water tank to hold the sink water.