Today I was playing the MM3D demo when I had a morbidly funny idea that I'd never thought of in all the years of playing Maniac Mansion. Since you can't progress beyond the green tentacle on the third floor, and you can't drain the pool to destroy the mansion, I decided on a clever way to end the game: a triple suicide. I simply gathered all the players around the microwave in the kitchen, nuked the jar of radioactive water and opened the oven door. Voilą!
Three tombstones in one fell swoop. The funny part is that you can still switch between the kids, who retain their inventory items in the grave. So you really CAN take it with you!