I know this forum is dead, but I figure someone might wander in someday to look for advice on this...
I've done this achievement on two different accounts, level 15 / 104k and level 16 / 100.8k. So these are some strategies I made that really helped me.
First randomly moving around and shooting things is not going to get you this achievement, the best that strategy ever did for me was 80k once....out of hundreds of attempts. Set your controller sensitivity to a few ticks below default, and move around with your d-pad instead of the analog stick. This makes moving a lot more effective, and reduces your chances of being killed from a random object.
You will want to stay near these long green lines, called spikes, when you are shooting a long spike you are invincible for a split second or so. If you stay on a spike to long you will die, don't start shooting at them until flippers are near you, if things get to hectic use your super zapper. NEVER use the second shot on waves 11+, you need that for the fuseball that gets on the rim at the end. So basically you want to camp near long spikes, which fortunately are usually in clusters.
Level 9 - You can do this two ways. Stay on the first upper right flat platform and just shoot, like 40% of the time you will make it off 9 without dying. The other way is to play the level normally, you will want to avoid a flipper falling ontop of you. Since the level is weird shaped they can kill you by falling on you wrong, the only other level like this is 13.
Level 10 - Fairly easy level with the spike technique, i usually begin camping at the bottom until things start coming. Jump on spikes when flippers get within 2 panels or so of you. If a tanker (pink box) comes at you jump on the spike immediately when it is near. You will probably want to use your super zapper when 5-6 things start coming at once, or if you run out of long spikes near you.
Level 11 - This will be the wave you spend the most time on, it's probably the easiest one since it's flat. It is also a valuable checkpoint wave, remember the fuseball will come to the rim near the end, so don't stay infront of it. If you get trapped with no spikes just stay still and fire, the game moves so fast that sometimes you will kill all the flippers doing this.
Level 12 - Score still really doesn't matter to much at this point, but you should have around 74-79k. This wave is heart shaped, but fairly easy to manuever around. Camp near spikes and quickly move around as you use them up (but there is plenty on this level). Beware of the fuseball near the end, remember to save your second shot for him so he can't get you!
Level 13 - This level is probably the main reason why not many people have the Maniac achievement. It totally craps on my strategy for 9-12, but that doesn't mean it is impossible. Move quickly with the d-pad counter-clockwise, never stop moving unless an enemy is close to you. Spikes arent as effective on this level due to the strange shape, flippers will just kill you anyway. Try to kill everything before it gets near you, use your super zapper if needed...remember to save the second shot for the fuseball.
Level 14 - If you made it this far the achievement is within striking distance, but don't get too happy as level 14 can still be tough. I camped near spikes like on 9-12, it's very effective on this wave. You should be pushing 90k at this point. If you died don't worry, you get a checkpoint back to wave 13. If you beat 13 again it gives you a 94000 point bonus, which will put you back at 14 with 98.5-100k, almost instant achievement!
Level 15 - So maybe you are determined to not have to go through wave 13 again, this wave is medium difficulty. Camp near spikes as usual, not much else I can say here. Remember watch out for the fuseball.
Level 16 - Only two people have ever reached this far, but if you managed to get here without the level 13 checkpoint (but you used the level 11 checkpoint) Then you are just a few hundred points away from 100k. I don't have many tips for this one, just hop on a spike fast and if you even think you are in trouble use the super zapper. I was around 99,600 at the beginning of this wave.
Sorry if it was a bit long! Took 2 years on and off to finally master throttle monkey, I will get a video up once I purchase a graphics card, I know sometimes visual helps more then text! Any questions feel free to contact me on xbl @ Rebornbobcat757